My sister never asks me to babysit

As the title states, my sister (35) never asks me to babysit. l’m 31, not married w no kids, her only sister, live 30min away, and have expressed interest to her in being a babysitter for her kids in order to strengthen our relationship and to personally learn about kids as I don’t have any of my own. I’ve expressed this several times to her, yet not once has she asked me to babysit. I’m starting to get offended that she doesn’t think I’m capable or reliable or anything other than the “fun” aunt who just comes over for occasional dinners and plays w the kids and reads to them.

Thinking about our relationship and the fact that she’s 4 years older than me, the only time I can recall her asking me a favor was planning her bachelorette party as I was the MOH. She has a helpful husband, and 2 sets of helpful grandparents that babysit often. She has other parents and neighbors that help, and also a couple of paid babysitters she uses. For reference, her kids are 5yr, 3yr, and 2 months.

I sometimes feel snubbed that she doesn’t take me up on my offer or let me help. Her kids love me, I live close, and I’m currently unemployed so I have all the time in the world to help…parents, am I reading too much into this? Wouldn’t you want to give your sister an opportunity to babysit your kids and help teach her how to do it? Or is the fact that she already has so much support and that I’m much younger and inexperienced in childcare enough of a reason not to feel comfortable asking me to help?

Anything I can do (other than express interest bc I already have several times) to build up to babysitting? I’ll admit that I’m nervous to do it solo at first bc I’ve never babysat by myself, but I learn fast and am up for the challenge. Thoughts from parents?

Thanks.