Because innovation requires taking risks. In the off chance those risks pay off, you are now massively penalized for your success. In that scenario you're much better off just selling the company or never starting one in the first place. This situation strongly favor incumbents by inhibiting competitors from emerging.

It's not that you can't have an exit tax, it's that it shouldn't be so out of tune with other OECD countries, so bureaucratic and so expensive to even process.