The reason we use 2.4GHz is because we're cheap. We've known of problems with it for years, with cordless phone makers making 2.4GHz phones, and with even the most well shielded Microwave oven causing interference. But we continue to use it because early 802.11a gear was expensive, and because "advanced" equipment like 802.11a repeaters was priced for corporate purchasing, when they cost $10 or so a unit to make.
Even after this, we still have 900MHz and 5GHz free and clear. Personally, I think the 5GHz Wi-fi system, coupled with cheap repeaters, is a better system than 2.4GHz, and I wish we'd move over to it. There's massively more bandwidth, interference from neighbors is close to impossible both because of walls and because the bandwidth makes it rare two networks will use the same frequency, and there's less interference from every day devices like cordless phones (even 5GHz phones, which are being phased out in favor of DECT anyway) and Microwave ovens.
If LTE-U both pushes us to move to 5GHz, and gives our mobile devices better coverage and more bandwidth, I'm all in favor of it.