2018 or not, there have been correspondence courses for ages.
(1) With online, there's no guarantee that the person whose name is on the transcript is actually doing the work.
(2) Offline, you meet other people in class who can be helpful and interesting. It's nice and actually FUN to interact with new smart people.
(3) Face-to-face and direct questions to a professor make recommendations and research advice more likely.
(4) Having a regular class schedule where you can turn off all of your electronic devices, listen to lectures, and take notes helps with motivation and retention.
I might be old-school, but that's my ten cents' worth.