I don't do anything sketchy online, but I use a VPN for the same reason I use HTTPS rather than HTTP, ssh rather than telnet, BTC/XMR rather than my credit card (when possible), and LUKS FDE rather than nothing. I value my privacy, and I want to fight the false perception that privacy-enhancing tools are only for shady usage by shady people.

Use a VPN for the same reason you close the stall door in a public restroom.

(I'm not necessarily agreeing with your premise that VPN usage has recently grown; I don't know that to be the case.)