He said why, he wanted to open source it with the mentioned exception.

I think there are also licenses that do that, and revert to full MIT after some time, but the author decided to roll their own.

What’s the problem with that? He can license it however he wants and the reason he mentions is perfectly valid tbh

Legal writing is like code: it's a specific domain, that requires special expertise to write properly.

If you see a problem with a non-programmer writing code, then you should see a problem with a non-lawyer writing licenses.