It's true that the capacity is nearly the same at the moment with docsis3.1, but consider that a docsis3.1 system that is using pretty much EVERY viable RF channel can just barely have the same capacity as a 10G XGSPON system that is using maybe 1-2% of the THz channels available in normal singlemode fiber.
If you look at a typical residential 16:1 or 32:1 split XGSPON system on an optical spectrum analyzer that's capable of all DWDM ranges, it looks gapingly empty. There's just a few channels used for the downstream and upstream with the timeslicing for the various CPEs' usage. And vast ranges of totally empty optical space.
What I find interesting is that your average residential user does NOT really use much more traffic in (in average Mbps per CPE or GB per month) if you give them a 2.5Gbps or 5 Gbps or 10 Gbps connection. I have plenty of 2.5Gbps and 5 Gbps and 10 Gbps customers. Maybe 1-2% of them are really heavy users. The rest of them use exactly the same amount of traffic as the 1 Gbps users, because the vast majority of non-technical residential end users these days have only wifi client devices. Finding someone who has a desktop PC with a 1000BaseT or 2.5GBaseT LAN port to do a proper speed test is maybe 1 in 50 customers.
Even if you've got people with 3x3 802.11ax stuff running in 80 MHz channels they're just barely going to approach 900 Mbp speed tests downstream one way.
If we had offered 10G FTTH to the home in 2002 the sort of power user who would buy that might actually try to run a small server farm out of their spare bedroom. But now it's 2024 and people who are serious about hosting their own stuff are doing it with their own VM/VPS/cloud based stuff, or by colocating a few servers, etc. They know that a residential last mile gigabit+ connection is not the best place for it. There's outliers and exceptions of course, but they're getting even rarer every year as a percentage of the total customers (eg: someone who wants to run a torrent seedbox from their house or something).
