[ithinkso]

As the comment above stated - so that the numbers don't grow too large

[CorrectHorseBat]

But why does that matter? They are as large as they are, a dot in between doesn't change that.

The only thing I can imagine is trying not to break scripts looking at the kernel version and expecting two dots. If that's the case it makes more sense to use the OpenBSD way and increase after 9.

[bdhcuidbebe]

Kernel version scheme has been bikeshedded for decades already, See LKML if you want to contribute further