Based on years of experience with @protonprivacy ... they take baby steps, to ensure nothing breaks. But they also give access to new features to users earlier as well. So if you want to join the fun earlier, you can opt-in.
Visionary users (not an available plan any more) gets access much earlier as well, and can often opt-in there too. When Proton opens up for opt-in at this stage, more publicly, they've decided to expand the scope further.
I expect that PQC will be enabled by default in 6-12 months - and then after some more time (2-5 years?) you can no longer create non-PQC keys at all manually.
Proton have far over 100 million users to care for. If something broke badly in the first transition, it would end up very bad for both Proton and all their users. This way they do more a controlled way of enabling new features while reducing the risks as well as lowering the consequences if something bad happens.
While I understand the annoyance of enabling it manually now, it the very end I'm pretty sure you'll see it will become the default with time.

