Because Apple and a Google created a market where there was none. It basically impossible to make money from selling mobile apps to consumers before them.
Had Verizon singlehandedly created the internet and had no real competitors they might have been able to tax it’s usage. Thank God that did not happen, though…
I am fine with them charging whatever they want, as long as they don't prevent competitors from opening alternative markets. The problem is the monopoly, not the price.