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.)
Honestly my ISP is to incompetent to run anything, DNS, billing, provisioning, you name it. I know because because we used to do consulting for them. I am confident that there is no way that they'd be able to monitor my traffic, they can't even tell if an entire town lose connectivity.
Incompetence finds a way when money is involved. Notice how parking violations are performed with zeal but police can not be bothered for anything else short of an armed robbery.
There're shady companies selling privay and others like mullvad. They don't take your name on sign up and allow for paying with cash or BTC and even Monero.
Even if they'd log your IP and traffic (which they say they don't) they'd know way less about who you are then your ISP.
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.)