Private equity firms typically own and manage a target firm for a number of years. In this time, the company's management and financial situation are improved before the private equity firm cuts the newly-successful company loose with an IPO, at which time the private equity firm earns a nice return for all its work.
In the buy, strip and flip situation, purchased firms are held for only a year or two before the IPO. This usually means that the firm's financial situation is virtually unchanged and, as a result, most of these IPOs do not perform very well.