The way I see it, PE is very long-term-focused investing, whereas a lot of hedge funds are not that long-term focused, with many not abiding strictly by value-investing and the like. Mutual funds, on the other hand, are relatively low trading-turnover focused, with often long-term holding periods. The pay is also similar to IBD and PE/HF (excluding outstanding performance at HFs). So why is PE/HF always the main exit opportunities for bankers?
By the way, I note that at top MBA programs, mutual funds are a very popular post-graduation career option, on par with HFs.
The short answer is there are just not very many opportunities to join the long-only side vs. HFs and PE. Voluntary turnover tends to be very low at most mutual fund shops so you may see something like 1-2 new analysts hired every year, which are almost always sourced through the MBA programs. Very rarely, maybe once every 3-4 years, will we get a lateral hire from the sellside (typically ER) or HF. Compare that to the multi-manager platforms that are basically always in hiring mode because the half life of their pods is so short. They are constantly rebuilding teams, promoting new PMs who need to staff up and blowing out underperforming teams. I don't have hard numbers for you but it would not surprise me at all if the larger platforms are hiring 30-50+ new analysts PER YEAR. That's like the size of the entire equity team at T.Rowe or Wellington and by the way most of those guys have been around for 10-25 years.
But yeah, it's not a bad gig so if you feel like that slower moving more deliberate investing pace is right for you, I'd encourage you to give it a look.