That answers it for many people, I would guess. Even without censorship, many ISPs have a much worse track-record for gathering and subsequently selling information than, say, Mullvad does.
Is it an absolute that Mullvad doesn't log/sell information? No, of course not. But they make a much more convincing case than my ISP does.
Geoblock avoiding is another common answer. My ISP also sends out letters if you torrent, which can be annoying to receive - Mullvad alleviates that.