1) Massive compliance overhead. Going public and maintaining public status can be a real nightmare.
For example staff generally "get" what a financial statement audit is about - are the numbers correct. And when they aren't everyone gets that a system should be improved. And the auditor makes some notes about areas to improve based on their work, and the difficulty and errors noted in checking the actual numbers. This is the audit most private companies go through - and it actually works pretty well.
A public company under SOX - now you have an audit of the numbers (great) and you have a kind of meta audit of the system (internal control) that got to those numbers (ugh). The cost / benefit of this second part is not clear to most staff. It's huge checklists, everyone get's checklist fatigue, and no one dares change a system after the auditors have been through etc. You literally can ask, why in the world do we do crazy procedures X/Y/Z? Because the auditors accepted it and we are too scared to change it. All critical thinking goes out the window. And folks start driving workarounds to the systems to get stuff done (double ugh and big actual risks).
Read some PCAOB reports for "audit failures". These aren't actual "audit failures" - no numbers were wrong. But it'll be things like - the auditor read over the calculations, checked underlying documents, recalculated numbers sat in on some meetings, but STILL didn't do enough to assess internal control over some calculation.
OK - I'll save the rest for later, but the idea that the private markets are the new public markets rings true to me. These are folks who can weigh actual cost / benefit of compliance cost vs losing money on an investment. Most are going to stick to something like a regular audit. Multiply by 100x in every dimension?