There are plenty of very good reasons:

zero-G planes are only mostly zero-g. They fly a parabolic trajectory, so their body actually rotates about the center of mass while flying.

Also, their weightlessness is not as well controlled as a drop tower's.

The cost you've listed is for a single passenger.

You know what's more expensive to build and operate than a pressure controlled tube on the ground? A pressure controlled tube with jet engines operated by pilots.