Because it does sounds good, right? So it must be good and therefore, you as well, right? And most important, its just so damn easy, right?
Its all a cycle, you see. Humans generally need something to stand up for, a cause to get behind, they usually find that in nations, family, friends and etc. But what happens when you live in a society that has it so good that it really doesnt have much what to fight? Well, you pretend that there is still something to fight for. To many in our society, they NEED that existential, emotional, moralistic and rebellious validation, it might be the only thing keeping them "sane" or at least socially functional. I dont think you truly understand how broken many of these people are and how hollow they would feel if this was taken from them. It feels good to say you stand up for minorities even if they have it good, you can ignore that and exaggerate things that you can construct a narrative around and, again, its easy. Most also dont really have anything to their names and its so easy to blame the world for it and thus not do anything meaningful about it.
Leftism is government approved store brand rebellion for the masses to consume so they can believe they are standing up for something and making the world better when they are actively making things worse. It doesnt matter because they do get what they always wanted, validation that they are, indeed, a good person.
I dont personally stand for any major political movement, simply going against the one that currently doesnt want me dead and destroyed. I dont seek the approval of others, I dont need the validation, I work hard everyday but most of all, I know humanity and the world are garbage and you cant really "fix" that, especially through politics as forcing those aspects of humanity to change did and always will be disasterous for all involved because, again, you cant fix humanity out of humans. All we can do is our best for ourselves and those we care about, focus on making the world better where it matters and humbly accept that, well, maybe somethings are fine as they and they dont need fixing.
They're really not. There are some absolutely brilliant leftists. They have a different way they view the world, different values, and different end goals for the way the world should be than those on the right, but that doesn't make them stupid by any means. More collectivistic, less individualistic. They advocate for oppressed groups and value compassion and human similarities, in their eyes.
Thats all well and good except that a smart person would be seeing that these good intentions are getting used and abused by powerful players. Most of them see nothing wrong in taking oppressive measures to "help" oppressed groups, thus raising the question if they ever truly cared about the act of oppression by itself or if this whole thing is in search of meaning and something to stand up for the sake of your ego. They are also the kings of bigotry of low expectations so they might show more racist tendencies than the ones that they accuse of being racist (like their constant usage of Latinx even tho latinos constantly tell them to fuck off with that shit)
edit: Lol, rated me Dumb. Cant force the horse to drink the water.