I've been using skiff. com for sometime, as they claim to be a fully privacy preserving app suite like GApps or proton. One thing I like is they provide 10GB storage even for free accounts, where proton eventhough much bigger provides only 500MB.
But that got me wondering... Are they trustworthy as proton? Is there a chanve they end up being a honeypot? Does data actually gets encrypted before sending to the servers in a trustworthy way?
Skiff is pretty good, I switched from proton over as they had a good one year promo and I found it fits better on what I need. The drive and page setup is pretty good too and so is the calendar. Overall I like skiff and they update and add a lot almost weekly. Big fan so far
Skiff licensed all of it's apps it at CC-BY-NC-4, why not change it for GPL 3.0 to make it a real free and open source software that respects user's freedom and mandates the fork to be free and open source. There's a difference between free software, open source and source available!
I presume the reason they didn't use GPL3 is because they wanted the attribution and non-commercial clauses offered by CC-BY-NC.
Not suggesting that they should not prefer to drop those clauses in favour of a copyleft free software licence. but you asked "why not" and losing those clauses is clearly an obvious candidate for why they might not want to.
A software using CC-BY-NC-4 is not a good option, as it was made for media. If skiff markets itself as open source, it should respect the guidelines of opensource( it's open source(https://opensource.org/osd/), you can read the 6th rule. It says the software should not be limited for commercial use.)