Ultimately, the blame does lie with SE because the system is one of SE's design. The player contribution to the problem is very small because it's only a very small number of players exploiting the loopholes in the system for personal gain. Most are trying to engage with the system as intended.
Where are you getting this "fact" that the majority of players do not care about housing? Have you individually polled every single player to get this information?
Right now, the system doesn't even accommodate the minority when you take into account how the available plots are open equally to FCs and individuals.
While the new system doesn't cut out RMT and multiple house owners, it's not going to be as easy to acquire multiple plots going forward as you make it sound.
The RNG of the lottery itself is going to be a big hindrance, especially as the initial supply of houses dry up and we're down to a few plots available per lottery period. Having 50 entries isn't much advantage if you're competing against 1000 others.
People bring up the ones they're most familiar with. Not to mention that Mateus was done long before the 4.2 housing changes while the Lucis set up was done entirely after since Spriggan was a new world.
But you're right that those aren't the only ones. I saw a lot of similar set ups when I was doing a world wide census back in 2019. Didn't matter where I was, every data center and most worlds had similar set ups operating in at least one ward if not two or three. When you see the ward filled with FCs using the same tag and that were established after January 2018, you know you're looking at someone abusing the system.
Spriggan (and Twintania) might have had a surplus of available houses at the time but the rules were still already in existence. One personal and one FC house per world per service account. I highly doubt there's a separate service account for each of those houses.
The use of a bot program might no longer be necessary but all those characters still exist and will still be entering into the lottery.
Very likely. RMT isn't dumb. They watch for opportunity and plan ahead.