Troy is not primarily motivated by money anymore; he has plenty [1]. What's most important to him is that HIBP is run the way he wants it run, but with more resources than a single person can offer. He's willing to pay the "biggest bill in his life" in order to preserve that vision, which honestly just increases his reputation as a person you can trust. He can make those kinds of decisions because money is not the main issue.

[1] https://www.troyhunt.com/10-personal-finance-lessons-for-tec...