Out of interest, what's the driver for 5G home Internet?
Depends who you ask. For myself, it was to save money whilst having a short contract commitment alongside the benefit of being able to take the service with me. In theory and even in practice in my own case, 5G broadband is faster than FTTC (excluding G.fast). The catch was, for me, the poor single-thread performance during peak hours that ended up being the main reason for cancellation.
I think the appeal is the cost, at least with Three's broadband. But it is also very convenient to just plug and play (and a bit of adjusting to find the best signal) if you live in area with coverage.
... are there areas where you receive 5G but there's no decent FTTC or FTTP coverage?
They do exist, even if they are rare. Though, what should be considered is that even if there is an area with decent FTTC or FTTP, there may be one or more practical reasons to why someone cannot subscribe to it; permission issues, lack of capacity, install not possible due to (x), etc. In those cases, it is easier and quicker just to get 5G (or 4G) broadband.