You're right it is not 100% for money but I'd say about 95% is for money. The networks can handle it.. If we go back to what AT&T said... 98% of their users don't use 2 GB... So... That's 2% utilizing it a lot when they had unlimited... And you're telling me it's not mainly about money?
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I'm not going to dispute the fact that carriers make boatloads of money. They do. I'm not going to dispute that the current bandwidth allocations are pitifully small. They are. The cell companies are in an unregulated oligarchy, they're making hay while the sun shines. It's very much about the money.
But there also is a certain amount of reason involved. With LTE, a single phone can take up the backhaul for an entire rural cell tower. And if too many people use full-out LTE on a tower, even one that has clustered dark fiber direct to a core Internet router, the tower can only broadcast on so many frequencies at a time, and towers that use the same frequency have to be separated to eliminate crosstalk (hence why all the carriers went whacko bonkers trying to buy more frequencies a few years ago).
When AT&T introduced the iPhone, everyone and their twice-removed cousin pissed and moaned about dropped calls, slow data, etc etc. And that was on their HSPA+ network. AT&T has since put in billions of dollars in upgrades to HSPA+ and started LTE deployment, but they also learned that even if 1% of their customers used their HSPA+ connections full-on 24/7, not only are that 1% of customers unprofitable, a half-dozen of them at a specific tower can reduce the quality of the experience for everyone else on that tower. Bad experience = defecting to other carriers.
T-Mo and Sprint don't have enough people connecting to each tower to worry about this, yet. Heck, around here, T-Mobile is EDGE and Sprint might as well not exist. It takes a LOT of people on EDGE to do any serious degradation to quality on a single tower. It probably takes about a dozen on HSPA+. It probably takes about 5-6 on LTE.
Until unlimited spectrum and unlimited backhaul become available, the only carriers who will be able to offer unlimited service are the ones that have far more capacity then their current demand requires, and they can use that overcapacity as a selling point. But if enough people buy it, they'll start running out. They'll start by kicking off the heaviest, most unprofitable users (just like AT&T and Verizon did). Then they'll introduce a cheaper plan for those who want to accept limited service and don't use 400GB a month (just like AT&T and Verizon did). Then they'll eliminate even being able to buy new unlimited plans and start throttling usage for those on them (Again, AT&T, Vz). Then they'll do their best to get people off the unlimited plans (AT&T/Vzw).
But, even so, money is the significant motivator. Having a subset of customers who are paying the same as everyone else but costing the company more money than they pay, and/or degrading the experience for everyone else and forcing the company to pay for expensive upgrades to keep a decent customer experience is bad for profits. Jettison those customers and you make more money.
If you get a chance to look behind the counter at most local buffet restaurants, they often have a series of pictures of people the employees are instructed to refuse to serve. These customers are either really big eaters to the point where they lose the restaurant huge amounts of money, or have a habit of wasting large amounts of food (taking ALL the crab legs, eating one or two, saying they are full, and throwing $75 worth into the trash uneaten). Sure, there are hard feelings, and occasional bad publicity, but there are some customers you just don't want and will take some bad publicity to avoid serving.