The reality is, they’re pushing out a beta…. something that is not designed for 99% of users. They push to 2A, it guarantees them the biggest pool of testing users to refine, build and refine for Phone(1) & Phone(2). The point above is correct, it allows for a better, more stable release for the flagships.
It’s also likely they’ve done most of the OS testing since early development on the 2A as it’s their more recently device. There’s also bigger complications with (1) & (2) because of the bigger/varied glyph interfaces, all requiring more time for refinement/development..
They’re a small(er) company, probably assigning a large percentage of their dev resources to getting OS3 right, we shouldn’t expect that they’ll have everything ready all at once. The reality is, if they’d had come out and said beta in December for all devices, people would have cried out that December is to far away, they’re getting an iteration of OS3 into the hands of some users and, now users are complaining that it yet support their device. Honestly, no matter how they spin their available plates they won’t win.