You make some fair points but DOTA 2's community isn't full of saints. I agree that LoL's players might skew younger and DOTA's will skew older but the same bile will come from both communities. I can't tell you the number of friends I have that have been turned off by both communities attitudes towards new players. I'm just at a loss as to how either game continue to expand despite the attitude of communities.I think it's honestly just age. DOTA players tend to be older, because they've been with or around it since War3 came out 11 years ago. League of Legends just skews really young, all over the place, but really, really young. The vast majority is teenagers, skewing towards pre-teens, even. DOTA 2 tends to feel more around 20-somethings or even younger 30's, just an older and more mature community all around. I'm purely making this shit up based on personal experience, I don't have any sort of demographic numbers for LoL or DOTA 2, as if such a thing existed.
I think it's a pretty fair hypothesis, though.
You can just "feel" the way that teenagers talk when you're playing LoL, as it's the most social exposure I have to that group pretty much at any time. It just feels like high school, or sometimes even middle school. I'm so past that shit, it's embarrassing.
I'm just basing this off personal experience as well. I prefer to play LoL with my friends over DOTA because I just don't want to go through the hassle of learning new champs/builds/lanes again.