Gigabit LTE means that you'll be able to use up your entire high speed data quota in less than a minute, unless the carriers finally update their data pricing models.
How is it that we've ended up with $10 for 10Gb or less of data now for about ten years? In the meantime, we've gone from inefficient EDGE to unbelievably efficient LTE, with HSPA+ available now for, what, the last five years on most GSM family networks?
Yet the data prices haven't budged. The carriers have more bandwidth than ever, more efficient ways of using it than ever, but they still think they're running ancient EDGE or cdma2000 networks.
Easy - profits.
Remember just a few years ago when people paid 25 cents per text? And some even paid another 25 cents to RECEIVE a text? Same reason - it was a massive profit center
Then texting stopped being a thing - with many ways to avoid it been iMessages and IM apps and Hangouts etc which used much cheaper data instead of SMS. Plus competition made it such that carriers started offering unlimited text plans for $20 extra. And of course, they realized they had a new profit center - data. Even better, they charge by the kilo and not kibi, and for good measure, they toss in the OTA headers as well in the byte count.
So yeah, they're charging because they can because it makes them massive amounts of money. On the bright side, they do adopt the new technologies quickly in an attempt to make you overuse your data plan and pay even more outrageous overage charges.