It feels like there should be a way to tax these startups that exist as vehicles for cash grabs, but are not profitable.
If you literally mean people (as in employees, executives, ect), they already are being taxed on income.
Unprofitable businesses always have expenses for labor, materials, ect. The distinction is that the company and owners arent making money, so they dont pay taxes. Those that do make money naturally do pay taxes.
What is the hard part to square?