Sure. You don’t need that many blocks to build a large keep. Hell, why stop there? After all, you don’t even need a large keep. Or a keep. In fact, on a PVE(-C) server, you don’t need anything bigger than a small house with a small yard where you can put one or two smallish thrall or animal taming stations.
That should be enough for anyone, so why not force them to play that way? The only thing that should matter is what you think people should be allowed to do!
Some people like to collect. Others like to fight. Others like to build. There are those of us who like to build and are perfectly capable of building something that exceeds the arbitrary limit you pulled out of your inferior dorsal orifice, without bothering anyone or impacting the server in any significant way.
Proof? I have personally built a castle, on an official server, that used 13,819 pieces, covered less than 1/4 of the grid square, and never bothered anyone or caused performance problems. It had all 6 shrines (this was before Zath was introduced), a greater wheel of pain, an armored taming pen, a map room, and all the crafting stations with a decent level of redundancy.
There are those of us who like building something big and intricate, yet are capable of doing so responsibly and without bothering anyone. We would hate to have our playstyle ruined just because some rando on the Internet forgot, among other things, that there are three dimensions in this game, and didn’t think of the fact that the number of pieces doesn’t equate the base footprint because you can also build up.
Look, just because you can’t imagine how anyone could get up to more than 10k blocks without “covering a map square with foundations” doesn’t mean that it’s not possible. I mean, we haven’t even touched the fact that one player could build more than one building in more than one location, again without bothering anyone and without blocking content and without impacting the server performance, and blow your 10k limit that way.
The 10k block limit a half-baked idea you didn’t bother to think through, it prevents an extremely narrow class of problems without solving their root cause or preventing any other related problems, and it ruins a whole bunch of perfectly reasonable playstyles.
To add insult to injury, the problem you’re so up in arms about already has a solution: report the megabases. Yes, it actually works, especially if you describe what those megabases are blocking and include appropriate screenshots.
There might be many things wrong with the current official server administration process, but this is one of those few things where it absolutely shines. I’ve had no qualms reporting stuff built by chuckleheads who don’t care for anyone else on the server, and it always got removed within a couple of days from reporting.
You know what also helps against such constructions? Reporting them.