Sucking it out is faster because there's no need to jack the car up or put it on a lift, nor do techs need to remove 4-8 screws holding on the sound encapsulation panel beneath the engine. It's all in the name of speed, you see. :p
Personally, my cars get changed once every 12-24 months and I drain it. I think that's a good time to inspect the undercarriage and thorougly clean off all oil residue, so I can locate little leaks (I have fixed all the larger/messier ones already.)
FWIW, the sucking really does pull out as much - or more! - than draining. The reason is, the tube goes ALL the way to the bottom of the pan, and sits extremely close to the bottom. The drain plug is in the *side* of the pan and is probably 1/8-inch above the bottom, leaving a few cc's of oil in there. We're probably talking about less than 1% of the total oil capacity of the engine though - absolutely meaningless in the context of routine oil changes.
YMMV, etc...