Your reasoning is correct if you think about negotiating options, or going all in on a trade, but its not quite right for stocks. The borrowing rates for MSFT and NVDA - even for a retail investor - are less than 1% yearly. So if your view is right you could hold a short on them for years. The market cap for these companies has already incorporated a large capex investment for AI DCs. As long as you use a reasonable rebalancing strategy, and you are right that their current investment in AI will not pay off, you will make money.
Mind you, this is a view that exists - a few large hedge funds and sell side firms currently hold negative positions/views on these companies.
However, the fact of the matter is, fewer people are willing to take that bet than the opposite view. So it is reasonable to state that view with care.
You might be right at the end of the day, but it is very much not obvious that this bet has not (or will not) pay off.
Won’t you get margin called if the stock goes up in the meantime?
And I don't know, because I have about 60 minutes a week to think about this, and also good quantitative market analysis is really hard.
So whilst it may sound like a good reposte to go "wow, I bet you make so much money shorting!" knowing that I don't and can't, it's also facile. Because I don't mind if I'm right in 12, 24 or 60 months. Fwiw, I thought I'd be right in 12 months, 12 months ago. Oops. Good thing I didn't attempt to "make money" in an endeavor where the upside is 100% of your wager, and the downside theoretically infinite.