Every step taken by the nonprofit leadership has to be, (or at least seem to be at the time), net positive for the stated goal of the nonprofit. To be legal, the IPO needs to be a net gain for the nonprofit.
It can easily be that, if they believe that the capital it raises increases the long-term value of the company by a greater multiple than the proportion of the company that is lost from the nonprofit to outside investors.
The primary example of this is Novo Nordisk (the Ozempic company). Their largest shareholder is, through an intermediary, the Novo Nordisk Foundation, which is one of the largest charities in the world. Nordisk used to be a charity that owned 100% of it's own labs and facilities, but in 1989 they realized that they were just too small, and would get trampled by larger international players without greatly increasing their scope. So they made their subsidiary go public (through a complex merger, not an IPO), and now only own 28% of it, instead of 100%. But, in large part because of the capital that going public brought them, despite constantly distributing money for research and charity, that's 28% of a company that's more than 100x bigger that what they used to be. And they retained 77% voting control.