There are a lot of reasons. Most of them would fall under a broad heading of having never learned that it was either safe or a good idea to ask. At the very least, I wouldn't get what I asked for, and at the very most, I'd be in some kind of trouble. In my family, this did not extend to stuff. I could ask for and get stuff pretty easily. What I didn't learn about was how to ask for what I needed emotionally in a family dominated by PTSD and alcohol. And so now I'm learning for myself.
First off, this is scary. What if I say, "I would like ......" and they, my music friends say, "So what?" or "Who cares what you want?" They would be kidding, and they would play what I asked, especially if it was my turn to pick the song, but still, sarcasm has a nasty bite to it. Crossing this tender portal into asking for what I want, the last thing I'm looking for is being shot down.
Sarcasm. I used to be sarcastic and it still shows up, in a milder form, when I feel defensive. A past teacher of mine told us that sarcasm comes from the Latin sarc, the tearing of flesh. That's what it feels like, when someone is sarcastic, and I apologize right here and now to everyone I was sarcastic to. It is a defense against feeling and a defense against kindness.
Asking for what I want makes me vulnerable. Not just me, obviously. It makes anyone vulnerable to ask for what they want. And if I don't ask, how will I ever get what I want? I will, as I did a few days ago, hold other people responsible for my feelings. In a perfect world, I would have learned decades ago how to ask that my needs be met in a healthy way. And so, once again, the "world's oldest toddler" category feels just right..