I don't think it ever was. I'll have to check, but I'm pretty sure this has not been how it's worked in any D&D edition. The standard has been, "You are level 12. If you somehow obtain a castle and set up shop, you'll start attracting followers." A castle doesn't just plop down out of the sky.
Name level is the point where "If you build it, they will come." You do still have to build (or buy, or capture) it.
My point is that it shouldn't be a class feature. Domains and followers would count as treasure or purely level based quest rewards.
A small castle would be a 10th level appropriate reward or purchase. A band of thirty loyal goblin followers would be a common resource of a 5th level adventurer. A devilish blackguard pact is available to a 6th level evil character.
One guy gets a flaming sword, another gets a mansion, and the last guy attracts an apprentice and twenty little scaly dudes who bow a lot.