It is economic to move massive stuff about in open space, which is what you need for an economy to attract people. The gravity well is a huge cost. You can make a profit by sending down the gravity well but going back up tends to be a huge expense.

You can (relatively) easily simulate Earth level (or close) gravity. Low gravity causes health problems for adults that spend significant time in it. I'm not sure what would happen to children growing up in it, but it could be far worse.

There's a lot of stuff in space that isn't in a deep gravity well of a spherical body. For instance mining asteroids enough to have a self sustaining manufacturing base at micro-g could allow for the earths manufacturing and power generation needs to be met somewhere that's not on the Earth, decreasing pollution.

There are asteroids about as close or closer in delta-V terms. Mars is the easiest other planet, but planets just aren't as useful as asteroids and comets right now, because of those pesky giant wells they live in.

And Mars in particular is better left pristine until we've had a really good look for signs of life.

I can agree that Musk's Mars mantra had its place when nobody was paying any attention but "Mars" meant something and "let's move to dead rocks" wouldn't have been appealling. It's nearing time to drop it, though, I suspect.