Why are telephone/internet lines less susceptible to surges than power lines?
Telephone lines are just as (if not more) susceptible to induced surges as power lines. So much so, in fact, that the phone company installs their own surge suppressors on every line. They're built into the network interface box that's installed on/in your home.

Therefore, any aftermarket devices installed by consumers are mostly redundant, and that's why they are not frequently used, unless the equipment being used is particularly sensitive.