They have 14 frames of startup, zero invincibility, shitty hitboxes, and the only way to make them safe is to hit with JUST THE TIP. Considering how slow they are (both startup and travel speed), it's quite reasonable to expect the opponent to either walk into or out of "perfect range" for the psycho crusher to hit just the tip. If you walk backwards, that's free sweep where Bison gets knocked down (a place he doesn't want to be). If you walk forwards, that's a free huge punish. And even perfectly spaced, lp PC is positive on block, mp PC is even on block, and hp PC is negative on block. How about this: how about you play Bison on a tournament level and occasionally use PC and let me know how well it works for you? Even lp PC from max range will get hit by DP FADC Ultra, Rog headbutt into Ultra, Honda ex-headbutt, etc.
Also, scissors are 2 hits, but you'd be surprised how easy it is to deal with empty scissor kicks at mid screen. In the corner, it's a different story, but you should really just be blocking in the corner against them anyway. At mid screen, if you stay at the distance where only Bison's second hit will hit, you can really use focus without any negative consequences. Bison doesn't have a normal that can deal with it. The second hit of scissor kick will get crumpled. Heavily scissor kicks or PCs will get punished if you just focus bait and backdash. You could try dash-throw, but that's a risk in and of itself. Also, let's not forget that every character in the game has several moves that just plain stuff empty scissor kicks. Bison's scissor kicks are good AND scary, but let's not forget that a large part of the threat comes from the 3 frame short that precedes the scissor kick.