Data caps are about charging for what is popular.
No company has ever really demonstrated a shortage of cell phone minutes, text bandwidth, connection count, data [bandwidth latency voluume]. The companies have only demonstrated a need to maximize revenue based upon what was in vogue.
In the early cell phone days, it was "minutes". Suddenly, minutes became cheap to unlimited (especially as a marketing tool: "friends and family", etc.) and we moved to extensive charge-by-the-text-message. Now, phones are more versatile as data engines (pictures, streaming music/video, GPS, etc.) and we are offered unlimited text and voice, with caps on the things we use the most. Excuse me, extensive charges.
Mostly in the major providers. At the same time they boast of the best and fastest and most capable networks. "We have the most but you can't use it."
Same thing with the home data providers (internet providers). Capacity grows beyond use, perceived need/use increases, and now we are seeing the two financial vampires appear: data caps and bandwidth limitations (no network neutrality).
There is no shortage. This is not a supply-and-demand curve model. This is a monopoly-and-demand model. With limited suppliers acting in an unstated collusion, we have the movement towards pricing models that focus on today's usage patterns. "Last year we drummed up the demand by offering unlimited data, now you want it so we're going to create an artificial scarcity and charge you for it."
Sadly, as monopolistic as these services are, they are not treated as utilities. They should be. A quarter-century ago they were a nicety. Now they are an essential part of the functioning/growing society/economy, and should be treated accordingly. Doing so would increase stability, access, and overall functionality.