Besides money, entrepreneurs invest a lot of time and energy.

Buying on one market and selling on another is not much more than gambling/speculation/trading.

Seems like a real stretch to call it entrepreneurship.

And, importantly, it's also their money. Perhaps personal, perhaps a loan. But they don't get to just pull in VC funding under the assumption that they can burn through it, close shop, and carry on like nothing happened. This is the real entrepreneurial risk.