First, why would anyone buy a .22-250 and then load subsonic rounds to use a suppressor?
I can tell you why a person would buy a 308 Winchester then use it to shoot subsonic ammo. Versatility. If you have a 1-10 twist in your 308, then it will perform well with any bullet that is 200 grains and lighter even subsonic. 1-8 twist is needed for greater than 200 grains subsonic. While the 22-250 example is a bit less likely to be used (in my opinion), it is not totally useless.
Some people do not want or need a dedicated subsonic rifle; they would rather adjust the scope or hold over for those rare times when they sacrifice range for stealth. It can be difficult to hit a target at more than 200 yards when subsonic.
I have a 1-12 twist suppressed 308 target rifle. I would not even bother to use subsonic ammo in it as I would have to shoot 150 grain to keep it from yawing. I have suppressed 300 and 338 whispers that are much better than any 1-10 or 1-12 twist .308 win when subsonic.