Because those cartridges are primarily varmint cartridges designed to shoot light weight varmint bullets. When you are shooting fast cartridges like the 22-250 and 220 Swift if you spin the bullet so fast that the light weight, fragile varmint bullets can literally come apart in the air.

Basically the longer the bullet is for a specific bullet diameter the faster you will need to spin that bullet in order for it to be stable.

Also the higher the bullets velocity is out of the barrel the slower the twist rate can be and still achieve the required RPM's to stabilize the bullet.

For example regarding the velocity.....
3000 fps with a 1 in 8 twist will result in 270,000 rpm's
4000 fps with a 1 in 8 twist will result in 360,000 rpm's

So assuming 270,000 rpm's will stabilize a specific bullet if you are going to drive that bullet at 4000 fps instead of 3000 fps then the required twist would only be 1 in about 10.5 inches for that bullet.