Why don't the P90 SGs have the tune-o-matic

I know the _some_ do, but in general they don't. If you look [here](https://www.guitarcenter.com/P-90-SG-Guitars.gc) 5 of the 6 models have a compensated wrap-around bridge, and only 1 has the separate tune-o-matic bridge and stoptail. Then if you just look at all the [SG listings](https://www.guitarcenter.com/Gibson-SG.gc?filters=condition%3ANew) the humbucker models pretty consistently have the two piece system.

But then when you look at [P90 Les Pauls](https://www.guitarcenter.com/P-90-Les-Paul-Guitars.gc?filters=condition%3ANew), it's much more mixed with both bridge styles.