What regulation makes it so that a large private company would have to go public? You have it backwards. Increased regulations make it more burdensome for a company to go public, driving companies like OpenAI to remain private. If you made it less expensive and burdensome to IPO (decreased regulation), you would see companies go IPO earlier.
This also coincides with a growing market for private credit and VC which certainly helps companies stay private for longer.
This also coincides with a growing market for private credit and VC which certainly helps companies stay private for longer.