It's not just the raw speed, but now, instead of 2 or 3 devices on 4G per household, we may end up (in the future - they plan for tomorrow, not for yesterday) with 5 or 10 devices per household. Imagine if each of your light fixtures was on 5G? Your appliances? Your garage door opener? Your front door? Maybe even your mailbox (is there any mail in it or not)? 5G is designed for much smaller cell areas, so it can handle the few hundred on your block, but not the tens of thousands in your town. 4G may be handling the whole town. Put 10,000 devices on that and your speed won't have G or M or even K after it - it'll be in bits per second.