Why dont we street/strip racers run these? Is it because they cant handle the excessive torque?

Maybe:
1. They are old school
2. They are not cheap
3. They are not common/understood
4. They are not efficient
5. They can be heavy
6. They do not handle a lot of torque, especially with slicks/heavy car
7. They are on the large size regarding fuel cell placement

But they look cool, and are really quick change, and I've considered using one

I know the roundy rounders use them and unless they hit something, they seem to hold up quite well.. and it sure would be nice to set up the rear end for cruizin to the track, flip over a gear or two to run down the track..

Ive used a quick change and they work great, i used one in a car with a iron headed roller 340 it went 6.50s in 1/8th mile at 108, noone heard a car use all 3 gears in the 1/8 before, i think i geared it 5.83 or maybe it was 6.00, they can be built with all aluminum bells and tubes or with steel tubes gundrilled axles and any width you want it. they are around 1700 new but can be bought for a couple hundred dollars out of a wreck circle track car, Id buy one right now if i could locate one they are very user friendly and indestructable.

I have heard that they are great for street-rodders and light-weight drag cars ..... but a heavy stick-car .. no way.

But I have no personal experience with them. I would consider one myself .. if they are more durable than I think they are.

We used them in the sprint car I worked on. A few reasons not to use them on a drag car: They are not very strong, definitely not efficient, they are rather long so you might have clearance issues, and I believe most importantly, most of them are made of magnesium which makes any machining on them dangerous, so you would be advised to pay someone to do it, which gets expensive considering most people don't want Mg filings all over their shop.
Keep in mind on a sprint car, it is under very little load because the tires are always spinning.