What makes you think they don't include the price of the OS when you buy their hardware? In fact, that's how many justify paying a higher price for Apple products - you get macOS, Pages / Numbers / Keynote, iMessage / Facetime etc. That's also why they stop supporting old hardwares after a period.

Yes and no. I'm sure they'd lose approximately some customers if were as easy to install macOS on commodity hardware as it is to install, say, Linux.

That is already true anyway with OSX86. I have known a number of people too poor to afford macs that rig up a hackintosh.

Apple has never stopped the DIY crowd. Their core market is the people that want the support and the branded aluminum.

That’s not strictly true. It’s hard work keeping a hackintosh working. I think apple is part of that.