Believe me, your wireless companies would like to retire the old protocols as fast as they can scrape up the capital budget, at least in the cities and medium-large suburbs, though less so out in the boonies.
The issue isn't just selling you an iPhone N+1 to replace your iPhone N-2 or have your tablet hit your monthly bandwidth cap in 2 days instead of 5, it's mostly that the newer protocols use their radio bandwidth a lot more efficiently, so if they can migrate the 2G and 2.5G users over to LTE or at least 3G, they can reuse the spectrum that's tied up handling older-protocol users.
They'd also be happy to migrate HSPA+ users to LTE, partly because of spectrum efficiency but almost as much because everybody's marketing says that "4G is Much Better Than 3G", so they're stuck scrounging up bandwidth to reallocate to LTE without messing up the HSPA+ users who haven't migrated yet and who might change carriers if their service degrades.
(Disclaimer: I work for AT&T, but not in the cell phone part of the company, this is my own opinion and not the company's, blah blah blah, and as far as I can tell, all the major carriers are roughly in the same bind on this issue, though the non-GSM carriers have extra incentives to move to LTE.)