Perhaps I missed something, but I wonder why WP didn't just include ACF functionality in WP Core from the very beginning?
Why fight in public when you can just commoditize your dependant competitor?
Why fight in public when you can just commoditize your dependant competitor?
It sounds like a reasonable philosophy until you see just how many basic CMS features it's missing and subsequently how many sites are running 20+ poorly-coded plugins that spam the dashboard notifications and have numerous PHP vulnerabilities.
Doing as you said is much smarter, but maybe takes a bit longer. My guess is Matt was reaching for some way to "hit them back" quickly.