Devices like lower end tablets often have 2 gigs of ram and 32 gigs of flash, which would be problematic because a 64 bit version of Windows uses 3-4 gigabytes more disk space, which would be further amplified by needing that much more space for the recovery partition. These devices are useful, if limited purpose, so putting a 64 bit OS on it doesn't make a lot of sense.

Here's an Intel blog post from last year talking about it: https://blogs.intel.com/evangelists/2015/07/22/why-cheap-sys...