It's also more complex than simply measuring how much of the securities lending revenue ends up back in the fund.

Most of that 60% for Fidelity's funds don't end up back in Fidelity's pockets either, but instead in the pockets of the people who borrowed stock from Fidelity investors in the form of rebates. You can understand this like: the borrower puts up 100-105% of the collateral and so should get some portion of the short-term rate on that cash. It's not clear why the disparity exists between Vanguard and Fidelity though.

iShares is truly different where they actually take 15-30% of profits for themselves.