system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 : How do companies go public?

And more specifically, what drives that decision and who pursues the IPO for that company?
gpt
The biggest driver behind going public is the need for funding. At some point, a company may not be able to fund their growth with their existing financing (investors, bank debt) or, more importantly, it's too expensive. That's when management and the board of directors explore going public. To do this, they seek the help of an investment bank, who then determine a valuation and court investors. Investment banks actually hold the risk for the shares, meaning they buy the shares first, sell what they can and hold what they can't. 

Market conditions drive supply and demand which drives company valuations up or down. Lately, companies have decided that there is too much risk to go public.