Rotaries are awesome, nothing else short of a jet can achieve the same power to weight ratio.

That said:

1. If the rotor wobbles (I mean side-to-side, not the up, down, back, forth wobble they're suppose to do) it rubs a little trail in the end-plate which the side seal can't really seal up. Pistons wobble all of the time and they do rub the cylinder, but the wear is uniform - it's a cylindrical wear pattern in a cylinder, so the rings happily take up the difference. "Piston slap" is the sound of pistons that are so loose fitting that you can hear them wobbling around inside of the cylinder. Rings do a lot.

2. Apex seals require some very clever springs to push them out against the housing, piston rings are themselves springs, they're round, and they naturally push on the cylinder.

3. You need both apex seals and end seals because the rotors need to seal against both the housing and the end-plates. From a sealing perspective, you can't beat a piston, it's one surface that wraps around in a circle.

4. There's no way to get oil to the rotor seals without burning it. In a piston engine, the top of the piston is all business, but the bottom is oily goodness, so keeping the rings greasy is just a matter of letting a tiny bit of oil leak by. In a rotary, every side of the rotor is all business, so the only way to get oil to the apex seals is to basically treat it like a 2 stroke.

So as cool as they are, it's not a conspiracy that we're still using pistons.