The oil is sucked out at the dealerships because it is much more efficient for them, thus it makes more money. Draining oil from the bottom and then taking it somewhere and dumping it in a tank is time consuming. The dealership service department is a profit center.

So, they are not doing it this way because it does a better job. They can do a good enough job that way, and it makes them more money.

It is still more economical and thorough for the DIYer to drain it out the bottom. The belly pans are no problem to remove and replace at oil change time.

Additionally draining the oil from the bottom gives you a chance to check everything underneath on a regular basis.

Have a great day,