Planets tend to already have people on them who might object to us tiling the land with factories and also come with gravity wells that we need to lift things out of although that's a lesser concern.
I feel like Denva would have concerns if we tried to build 1,500 Manufactories on their world, unless we promised to hand them over to their control at some point, which is maybe an option but still a tough call.
The locals here however, are in no position to object. Neither is Denva or anyone else we care about. The Imperium may have something to say, but I expect we'd be sufficiently established by the time they found out that doing anything about it would require a major fleet action, and could be politically impossible if we roll out the story about being a revived ancient from the dark-age of technology who woke up on Denva, joined their Mechanicus, rose through the ranks with our amazing knowledge, and have now claimed this system for a new forge-world.
And we're not "starting with a ton of extra manufacturing capacity" in Denva, we had factories there but gave them to the locals when we left. I doubt they'd be pleased if we revoked that gift.
