The point of mit is to get the licensed thing used as widely as possible. It breaks down any barriers to use

There are no barriers to use, except that you have to share the source code back, and give users the option to modify it. If you use it without modifyiing it, you can just point users to the existing public code.

The only barrier to use is that Apple disallows (A)GPL related libraries in any of their code, published through their main distribution channels to their platforms (mainly talking about apple app store here).

https://www.zdnet.com/article/how-to-avoid-public-gpl-floggings-on-apples-app-store/

But this is ultimately on Apple for not giving users the needed amount of control over their devices to comply with the license. This annoyingly common rhetoric that the GPL itself is a "barrier" or "restrictive" is just blaming the wrong party.

Now, even though I'm more in favor of copyleft, I can understand with the decision to license software or libraries permissively in order to be able to distribute them through the App Store.

gpl licensed is a game engine you want people to be able to freely use and modify but never make secret changes to sell

This is tricky because the GPL is fairly aggressive, and may require the entire game to be open sourced if it's distributed as one bundle. LGPL doesn't fight as hard for users freedoms, but also has some similar issues. Most game developers don't want to open source their games, so I think a permissive license is probably the easiest choice for a game engine.