Because nobody knows. This has literally never happened before.

99% of Bitcoins are being held by people expecting to sell it to someone else for more than they bought it for. That doesn't seem to be changing.

You just have to do a calculation involving the number of people on the planet to figure out when the supply of new suckers runs dry and the price crashes.

Doesn't that assume every person on the planet will own some BTC before it crashes? It also assumes the rate new people start buying BTC is constant, or even predictable.

The comment was perhaps a satirical take on the "BTC as investment" philosophy's implied endgame.

If more vendors would take BTC, I would gladly buy things using said BTC. I would rather do that than convert to cash and then buy.

If BTC has a good chance of doubling in value over the next few months, then how is it remotely rational to spend it?