The thing about dota that makes it so fun imho is that you can always inprove and learn new things, that along with patches that can basically make you relearn the game. I feel like people stop having a fun when they stop trying to improve. I had a friend that use to play all the time and rarely plays now bc he says all his games are bad or has stupid team mates ect ect. He just stopped playing instead of trying to improve and get out of the "trench"
Just my opinion about dota is that is constantly changing, games are different, and there is always something to improve on or learn that makes it so fun for me.