Mastodon should revamp the project's website homepage and promote a mobile apps with the closest Twitter-like feel or maybe a page for it without giving too many options (so people trying to promote it would share the link and people who aren't familiar with federation not think its weird "non-official" websites promoting multiple apps), these people just want convenience and most are mobile users.
I wish most would go to Mastodon but there are so many barries going from something quick and convenient like Twitter to something like a Fediverse social media, I think Pixelfed catches this issue better of looking closer to what people are used to (in their case, an alternative to Instagram) than Mastodon (alternative to Twitter)
The default iPhone app and sign-up process for the main instance is pretty darn straight-forward. I’ve never been a Twitter guy so I can’t speak to functionality, but it seems fine to me already.
Given everything we've seen over theast little while, including the process of non-profits getting taken over by their VC funded subsidiaries; that difference you see is almost certainly a matter of being at a different point in their respective profit timelines.