Actually, the number of sessions you got is what's really surprising to me. That's 7 game starts per day! Either your games are crashing often or you're switching games a lot every day. (Or Steam is going wonky.)
There are a lot of reasons for the game starts. For one, I play a lot of games that involve big jobs and to keep from being bored, I'll hop around and do a little bit at a time. For instance, I'm playing House Flipper and renovating huge, end game houses is kind of intimidating, so I might log in and do one room, then quit and play something else and then log back into House Flipper to do another room, etc.
Another factor is just being wishy washy. I may open up one game and a few minutes later think, "I'd really rather be playing Forza."
Do you mod most of your games or just a few of them a lot?
I think I remember you mentioning you had about 400 mods for Farming Simulator, so I'm guessing the latter mostly.
I can't remember, but I either had over 700 or 800 mods going on Farming Simulator, but those mods don't count in this because they aren't from the workshop.
I pretty much mod every game that has workshop support, but I don't know where they are getting the 1300 workshop items number from. I have a feeling that this includes everything I ever subscribed to (not just this year) and didn't bother to unsubscribe when I stopped playing the game.
Also, I'm guessing most of these mods are from Planet Coaster and House Flipper. These games have 'no script' mods that simply add an item(s) to the games, and it's hard for me to resist downloading these types of mods. I've got about 600 mods for those two games combined. As for the other 700, it has to be a "lifetime" sort of number.