Well german telecom tried to introduce caps into internet plans ~5 years ago at around 200GB. But that caused so much outrage, that they rolled back on that decision and ultimately you only get a cap on the cheapest of providers. I mean try downloading GTA5 and Red Dead Redemption for PS4/PC, and you have already used up your datacap.

Mobile Plans are so expensive, because we germans auction away the licenses for the Frequencies for billions.