Shortly before the free trial announcement, Elon said FSD training was no longer compute limited. They are going to be getting a metric ship-load of data from the free trials. They are going to be getting a lot of edge cases and they will be getting data from regions where data may be lacking (middle America).
Elon had previously (a year ago?) promised/said that as soon as FSD gets good enough (safe enough) for general use then he would be giving everyone a free trial. Until now, the price and the version hoop jumping were designed to limit the number of beta users in order to prevent inattentive testers from creating accidents that would be catastrophic PR.
The timing of the wide release wasn't based on whether people are ready to purchase or subscribe to FSD, the timing was based on v12 being ready for wide release. IMHO this was a necessary step on the way to actually solving FSD. I don't have the exact quote but 2 or 3 years ago Musk said that they need to actually solve FSD to make it a compelling purchase. You're right, FSD is still not solved, but this was a big step in the right direction.