See... I played games on PC as a kid, but gaming from middle school through high school was largely social. Like, if you didn't have controller skills, you weren't even fitting in with my friend group, because we were all playing competitive games with controllers. If you hung out with that group, you were going to get good at using them. Not even as a hard expectation... more just a matter of course. Unless you just enjoy getting mocked and having your ass handed to you by the same group of people every day.
It's funny, too. I am competent with KB/M, and I can even see where it is simply superior. I can also recognize how it's better if you're a game designer. A controller has to be simple and intuitive, by the paths the controller you're designing for gives you. A mouse and keyboard gives you more options for control schemes and gui/interface layouts. Having to design for controllers limits games, functionally.
Buuuut unless I'm competing seriously, I default to controller wherever possible. I'm basically an old man now, so comfort takes precedent over 'edge' or whatever. Yes, even shooters. With light assist and practice easing up to the highest sensitivity, you'd be surprised at the amount of speed and precision you can have with aiming and movement. Certain movement combos aren't as easy, and obviously the granularity and response time have hard limits, but it's really enough if you just git gud. And then you can enjoy the added comfort of not being physically confined while you play.
Do ya'll understand how nice not being coupled to a desk is? I don't want to sit up at a desk to play games. I want to melt in my chair. Hell, if you reverse the sticks, you can play upside down. That is the primary advantage. You're holding it in your hands, so you can take it anywhere. Though in all fairness... I have ADHD. Sitting still really isn't for me. Hard to squirm around with the mouse and keyboard.
Immersion-wise, I just find it better. The way hands interact with a controller works better for me, when it comes to forgetting that all of the actual interaction is with that object and not the things in the game themselves. This may be familiarity. People used to KB/M will have their immersion broken by hangups that aren't even hangups for me. I can decouple better with a controller. KB is for management and strategy games... for me, obviously.