I expect because they are trying to deliver a product that works well enough on a minimum setting that it doesn't alienate potential players. But to be this forthcoming and generating and giving code to those willing to push the boundaries (literally) is a very refreshing and great experience.
I expect there will be a new minimum spec for the larger maps as modders test them. And those with those specs can chose to run. But as CO said it won't be a supported feature, but more of a compromise to those who are willing to try.
That 1st part is true, but the last part won't happen. There will be no "new" minimum requirement for "larger" maps, as there won't be any official "larger" maps . They've said openingly many times that they offer
ZERO support for people who want to mod and try beyond the 9 tile limit they've tested and implimented. I suspect they made it easier to unlock now because of all the fuse people made. I sort of imagine it as a "ok, FINE! Now they'll see why we stopped at 9! mWha ha ha ha", he he

As ma2412 said though, gaining access to the extra tiles is just a small part of the obstalces to over come with beyond 9. I think people will find the simulation probably falls apart or runs a muck shortly there after. Also I think people forget the very hard wall/limit of 1 million population, which I imagine you can achieve within 9 tiles with some work, so more tiles is mote if that's the case. I "believe" a dev said that was a limitation of the Unity engine more than anything.
So congrats on 25 tiles, even IF you can get them to work, you'll eventually run out of people and won't be able to expand anyway.
Maybe there is a way to make a district ban buildings over a certain height? That way you can create a CBD (Central Business District)?
Yes, they've mentioned this before that you can limit the height of buildings either city wide or thru district options.