8 is old, 8.1 is relatively new, had no time to get as much share. Also 8.1 has new hardware requirements, so many people with radeon 4k series (for example) and older CPUs (CMPXCHG16b) were locked out. Good old XP and 7 always do the trick though, not to mention linux.
Windows 7 has the best features for old PC/Laptop x86. Windows Fundamentals has the best performance for old PC/Laptop x86.