Veltharis ap Rylix
Legend
Need to go back through their videos from early last week to double check the exact wording, but that was how I understood the matter.IMHO "character build diversity" is a strong argument against floating ASI by default. But has Wizards hinted that this is their reason for this rather unexpected change? It's plausible, but I wasn't aware that they'd addressed it.
They've had floating ASIs since Tasha's, but found that it was counterintuitively not resulting in more varied sets of character statblocks. Most people were putting them in the same places - implicitly, whatever they're class was good at - which is why they decided to tie them to backgrounds (albeit with more flexibility than how species-locked ASIs were handled previously).