Says you.
If you have the opportunity to make a bunch of money moving on to a new gig, hire your old co-workers, and work on new technologies like self driving cars[1], I'd say that's going to have a much larger impact than picking up a hammer and building houses Jimmy Carter style.
Also, using the Bill Gates, who's probably 2+ orders of magnitude wealthier than Singhal, as a comparison point isn't fair either.
[1]: Guessing on this one as I have no clue what projects he personally oversaw at Uber.
You don't have to be Gates-wealthy to be a philanthropist. Hell, I did some philanthropy when I was earning only $35k a year - I saved up $2k and sent out an invite to a dozen friends for them to do any short course of their choosing up to $150 and I'd pay for it. And that's small potatoes - there are thousands upon thousands of people out there working long-term as volunteers for good causes despite also being on or near minimum wage.
The idea that philanthropy is only the domain of the ridiculously wealthy is just bizarre.