Unlike most firms, Vanguard's funds own the firm, rather than the other way around. The funds are owned by Vanguard's customers, who transitively own the company. Vanguard "pays cost" for all the work its management and staff performs.
To illustrate how powerful this structure is, see Matt Levine's writing about "the fake moon landing of financial news stories": a claim by a former Vanguard insider that the savings accrued to the funds (and thus customers) as its result constitute billions of dollars of taxable income (under the IRS whistleblower rules, some percentage of those taxes would go to the insider!):
https://www.bloomberg.com/opinion/articles/2015-11-25/calper...
Bogle is a giant and a good guy in a field not packed full of good guys. RIP.