Every mobo I can think of has at least some 32bit drivers. There's components that simply do not require or use 64bit drivers, like CD/DVD, and because manufacturers need to fill every condition, win7-win10 usage, you'll still get basic functionality. Just as most budget type boards also have a vga port still, as there's many ppl who do not use or have a use for hdmi/display port.
About the only thing I can think of that's not supported at all by windows 10 is anything that requires DX9.0c, which was supported by Win7. But even that is an easy fix with a download from Microsoft.
Microsoft ended Active support for Windows 7 a little while ago, is now in extended support, until 2020?, which is basically just some security updates and bug fixes. Other than that, Microsoft is only offering full support for Windows 10.