Polymorph doesn’t say what?

I'm always kind of amazed that DND is such a big budget game that has so many weird problems.
- Don't need to hire proofreaders when people buy the books and post their own interpretations anyway!
  
  If not for that we wouldn't have story-driven adventures anyway. The game was initially focused on dungeon crawling.
- 5e is in this weird space where, on the one hand, it's loose and flexible, but on the other, it's designed around balanced encounters and precise readings of kind of a lot of rules.
  I found it an exhausting balancing act as a DM.
  
  Don’t worry. It sounds like WotC is planning to fix the issue with not enough people wanting to DM their jank by implementing AI DMs in their new VTT.
  They did say before that no one at Wizards was working on AI DMs, but it’s all but officially confirmed Hasbro had a 3rd party working on it for them. That’s why you gotta keep your eye out for those little loopholes. 😲
- If video published games publisher put out titles with gamebreaking bugs and expected the player’s computer or console to figure out what was wrong and fix them, there would be riots.
  I’m always kind of amazed how many people defend WotC putting out products with so many weird problems and expecting DMs to just shadow-patch the issues and not complain about it.
  
  Right? And a lot of websites provide a front end, but imagine if you had to look up the API docs, figure out auth, and do your own http post to reply to messages here. "it's more flexible that way. the DM can decide if they want to use like postman, or requests, or write their own tool!"

That's pretty funny. Once again a reason why D&D was not made to be played RAW.
- I always feel like even True Polymorph should require some sort of check or a pseudo-spellbook of studied creatures so that the user can only turn into creatures it knows well enough. Turning into anything the player can pull a stat block for is not only overpowered, it's downright immersion breaking.
  
  Well, true polymorph and mass polymorph at least aren't overpowered for their levels. Comparatively polymorph as commonly interpreted to be a "caster decides" effect, is routinely considered the best 4th level spell overall. It has better single-target save-or-suck disabling ability than banishment, it rival arcane eye in terms of scouting utility, and as emergency temporary healing or a combat buff it outperforms the 6th level Tenser's transformation.
  The only other 4th level spell that even comes close is the "caster decides" interpretation of conjure woodland beings, mostly because you get eight polymorphs for the price of one.
  
  True but you should be able to choose a little. When things like woodland creature are so random( and I guess know polymorph) its hard to form tactics around become rather useless. If you have a mean DM it can be a hazard like turning into something useless and not contributing to combat or summoning something that ether dies immediately or just clogs the initiative not helping.

The more I look into it the more I start to feel like it's entirely intentional. As OP mentions, the other forms of polymorph explicitly spell out you get to choose, but normal polymorph does not.
Also, while it's of course not directly related to DnD, there are some older dungeon crawling media that have both been inspired by DnD and been an inspiration to it that run with this interpretation. For example, in Nethack, a dungeon crawling game first released in 1987, polymorph is entirely random making it a gamble. At least DnD 5e caps the challenge rating so at worst you'd get another monster in the same ballpark strength as you had initially, in Nethack you could just as easily turn a goblin into a dragon.
- Powder does the same thing, unless you have a ring or artifact that grants you polymorph control.
  But, as an aside, a CR 𝓝 creature is intended to be an appropriate challenge for a party of 𝓝 level characters, not the equivalent in power to one of them. If you were to actually calculate the CR of an 𝓝 level character it's closer to ½𝓝 like in mass polymorph.

""I acknowledge the rulebook has made a decision, but given that it is a stupid decision, I have elected to ignore it""
--several people here probably

"Fine then. I cast Fireball instead."
"You know, it doesn't say you can choose which spell to cast."
- There’s a whole chapter dedicated to spellcasting rules. There’s a fair number of steps involved beyond just choosing which spell you want to cast. There’s a wide variety of reasons that might not work, especially since there no rule that allows you to change what you’re casting after you start.
  
  It doesn't normally talk about choosing. Like it says you can move during your turn, but not that you can choose if you move or where to move. If the DM chooses everything that the rules don't specifically say the player can choose, then they're practically playing the game by themselves.

Automatic disadvantage on your next roll for rules lawyering the DM.
- I personally just rules lawyer back twice as hard.
  Well, technically revivify requires you to target a creature not the corpse of a creature…
  Actually detect magic doesn’t exclude itself, and the passive detection is pass/fail, so unless you’re immune to divination…
  Oh, the demi-lich got errata’d to have more hit dice, but they never “corrected” the default hp based on the special Undead Nature trait, so now it actually has %60 more hit points than the stat block would imply.
  Sure, freedom of movement lets you escape these non-magical restraints, but you have to spend 5 feet of movement to do it and your speed is currently 0.
  A fair chunk That Guy’s tricks depend on a lenient or permissive DM/cherry-picking the most favorable rules & interpretations. If you don’t shadow-patch a bunch of fixes to make things work how people expect them to the game breaks down. If they want me strictly following the rules I’m happy to oblige, but I’ve never seen a powergaming munchkin who could withstand the amount of nerfing actually playing RAW causes.