I'd say it's only natural to get bored online only playing 1 game and focusing completely on it. You are basically staring at your screen, looking and numbers unfold. You can't make nearly as many reads, you can't really chat properly, you don't need to focus on how you act ect.
Lets make a simple comparison. How long can you hold a conversation online/by phone compared to talking to someone in real life. At least for me, in real life I always feel I'm running out of time when engaging in conversation with someone, while online or on phone 10-15 min and I can't wait to hold up.