There are reasons to play an RPG online.
People you have played with in person live different places and you want to stay in touch.
A particular game master or designer is looking for players and your only opportunity to play with that person is via online games.
You are house bound.
You are afflicted with anxiety, depression or some other psychological disorder that makes leaving the house too emotionally difficult to manage an in person game.
You are a game designer (amateur or professional) and you want to get impressions from people who have different tastes than you about the work you have produced.
Networking, brand marketing and generally “putting yourself out there” in order to build trust and permission from your audience.
There are others I am sure, but these are the main reasons that come to mind. I am going to assert that online RPG gaming should be a secondary thing. An adjunct to regular in person play unless you are unable to play face to face.
I’ve played online a bit. It was fun, it was better than a lot of things I could have been doing but it wasn’t better than playing in person. My current game group is great. Last weekend after the game, a local food truck was having an open house/pig roast at their commissary. Everyone that could make it, went and had a little barbecue and we hung out and talked about music and books and art and games. It was fun. We were in a place, together. You can’t do that online.