The community's complaints with PHP are far more concerned with technical matters relating to the language, runtime and libraries than how Zend etc have handled the usual issues in politics and project governorship. I don't think PHP has ever had a brouhaha anything like what happens in Java's JCP or the Oracle sale. Other platforms (like .NET) have their own foundations but they aren't taking seriously by the community because we all know the commercial companies that back the tooling are the ones that really matter.
...so what's the real reason for PHP suddenly switching to a Foundation-supported model? And why couldn't they entrust PHP with an existing and well-regarded foundation like Apache or FSF?
If you read the announcements it explains why they are doing it.
PHP is a community driven project, comparing that with C# or Java is a bit unfair because they are backed by companies worth billions.
What you describe about Zend I think that is more the old days before PHP 7. I don’t have the full picture of this but my understanding is that because of the failure of PHP 6 (never released), another group of developers from the community started to work with PHP 7 and I don’t think neither of them was from Zend.
Today there is an open RFC process and anyone can submit an RFC and then the core teams votes on it. If you contribute to PHP you can become a member of the core team.
If someone is unhappy with direction of PHP my advice to them is to start contributing, bug fix, write documentation, translate, write RFCs, implement functionality, code review etc. Why? because PHP today is a community driven project.
Announcement
https://blog.jetbrains.com/phpstorm/2021/11/the-php-foundati...
PHP Foundation
https://opencollective.com/phpfoundation
Accepts donations to help the development of PHP.