I think some of it is about the optics as far as raising future rounds. If you're a founder that has built a company with a valuation over $1B, raised a number of rounds, but really only proved that customers like your product at a price that's subsidized with lots of VC cash, living a lavish lifestyle could lead potential future investors to think that you believe you've already made it.

I think they'd prefer that you take the perspective that you've only really made it once you've made a profit for your investors. Or even, gasp, until you've built a self-sustaining, actually-profitable company. Otherwise investors will worry that their investment is in your lifestyle rather than a company that will eventually earn them a return on their investment.

Once a founder has built a company that's exited or doesn't need any more funding and is turning a profit, I doubt anyone particularly cares how they spend their money.