The passive-aggressiveness is through the roof.
To answer that, you're assuming that there's "fun" involved into unlocking new heroes. That's where the thing falls apart.
Not everyone is fine with being forced to play a very specific subset of heroes(less than 10% of the entire pool btw), until they manage to eventually get one they truly like for themselves. God forbid they want a second character as well, even more grinding. And so forth.
It neither is an excuse for "learning the game". You don't learn the game better by playing a certain character all the time. At this case i'd argue that it makes you play worse, since it restricts your PoV and doesn't allow you to get the feel of every hero.
For reference, the limited heroes mode that Dota2 has, to ease people into the game(optional btw), means that you won't get to play specific character, but you won't play against them too, if you want to. That's the right way to introduce options. Being thrown into a random pool of fuckall, with almost nothing to work with yourself is ridiculous.
To sum it up and conclude my point, grinding for heroes doesn't make you superior. It just creates dependancies between the player and the game that have very little to do with the game quality. To the point where you stay in the game just to unlock the next character, not because you have fun or even want to play the game anymore.
It's the same reason that you see people all over the LoL complaining about the game, but would cry buckets if their "main" would get nerfed(even if they have stopped playing or moved on). Hell, it's the entire reason that "maining" is a thing. It's not option. It's being restricted by the system so you're forced to play a specific hero because you unlocked them.
Liking stuff like this is akin to Stockholm Syndrome. You'll always see people complaining about this. But when asked why don't they move to dota, they don't have a real answer.
That's lazy. Being invested that much into characters that you can't go and being that knee-deep into Riot's shit that you'll believe a game is anti-fun, just because they said so, when you've had little to no first-hand experience. I'd argue that Riot rewards lazy as well, but that's beside the point and i've digressed.
If you want to keep something from this, is that the unlock system was considered good, because at 2009 it was the only serious "free to play" game that used it and it seemed fair, since every game until then was either paid(HoN and the original DotA mod was tied to wc3) and people were generally fine with freemium games(i'm looking at you Facebook). Since then, Dota2 has happened and it did it even better. People were just too invested into LoL to accept it.
Update your preferences or try to argue that people like to be treated like idiots, it is a fair point with LoL and Hearthstone being popular all over. I don't it's as much preference as it is peer pressure or personal investment.