My reason is that it’s extremely buggy. I find it looses the plot if you are moving more than 1 file at a time, and it often can’t find paired devices even if they are on the same network. Plus it’s over bloated with no default configuration. I.e. I just want to send files. I don’t want it to act as a mouse pointer. And disabling it for each and every device is tedious.
Granted it’s better than any other alternative apps I’ve found. Which is why it’s installed, even on my iPad.