The charges theoretically defray the cost of the phone system. Before mobile phones were common, people were stuck if they needed to make a call. Now, with most people carrying a cell phone, few people need a land line in a hotel room.
I occasionally have a lousy signal and an important call. If there is a significant charge for accessing a toll-free conference line, I have my assistant call me.
There are likely people who either don't pay attention to these charges and get a rude surprise at checkout or who don't care because they expense the calls.