Because they’re laden with so many features you will never use.

Just look at this motherboard for a PC. It has:
1 x 7.1 Audio I/O [perhaps, but i prefer my external soundcard]
1 x D-Sub [no]
1 x Line In [no]
1 x Line Out [no - why with the 7.1 then]
1 x Mic In [no]
1 x Parallel (LPT) [hell no]
1 x PS/2 Keyboard [yawn no]
1 x PS/2 Mouse [no]
1 x Serial (COM) [no]
1 x 10/100/1000 (LAN) [okay useful]
4 x USB 2.0 [you got me, yes]

Why do PC users always want this crap?