Please follow this guide, here:
Regressions are the bane of those hoping for good things from the later kernels.
For reasons I think most of us would not understand, the kernel development team will often remove elements from the kernel - perhaps that they feel are outdated or superfluous... but are actually still needed.
The kernel code is quite long, earlier versions were over a million lines of code total.
Not sure how long these latest ones are, but I suspect that the impetus is to shorten it where ever they can.