Because Bay Trail devices only came with a 32-bit UEFI making it impossible* to boot Linux. (*annoyingly obtuse to get it to work).
[Source](https://johnlewis.ie/custom-chromebook-firmware/rom-download...)
And I do sympathise with buyers of cheap tablets but by comparison, Intel had a couple of Bay Trail NUCs for which run 64bit Linux just fine.
As far as I'm concerned, putting 32 bit Windows on them is purely a business decision.