Because those signals are really high-speed, and the protocols are really complicated.
Doing the equivalent of "yank cable from PC 1, plug cable in PC 2" is just about doable at a reasonable price point. Anything more complicated either requires a bunch of expensive hard-to-source dedicated chips, or a bunch of hard-to-implement software solutions. Especially stuff like reliable keyboard-controlled switching or USB-C laptop connectivity is a nightmare.
In practice this means you either have to give up on features, or let the price balloon to unacceptable levels.
Doing the equivalent of "yank cable from PC 1, plug cable in PC 2" is just about doable at a reasonable price point. Anything more complicated either requires a bunch of expensive hard-to-source dedicated chips, or a bunch of hard-to-implement software solutions. Especially stuff like reliable keyboard-controlled switching or USB-C laptop connectivity is a nightmare.
In practice this means you either have to give up on features, or let the price balloon to unacceptable levels.