Several reasons. First, I love fabric/textiles. Always have, always will. Quilting gives me an excuse to buy it. Once I buy it, I have to use it, so, sooner or later, it becomes a quilt. Second, when I retired I needed serious 'decompression' from commitment to anything. I also needed something to do while I decompressed. Made my grandsons twin size bed spreads. Had no idea what I was doing, but they turned out ok - 12 years later, those bedspreads are still in use, so I couldn't have done too poorly.
Then my Mom went into her final 'decline' and needed someone with her 24 x 7. I wasn't working, so my DH and I became the care takers. Honestly, I enjoyed it. As one of 8 kids, I never had her to myself before that! But I am not the type who can just sit and watch TV all day, so I went to Walmart and bought some $2 fabric and made my first quilt. Mom was going to help me. This was her help: "I've forgotten more about quilting than you'll ever know!" She was right. She'd forgotten it. But she was an excellent quilt inspector.
After 2.5 years of non-commitment to anything other than my Mom and my grands, I decided I had to be part of the world again and joined two quilting groups. I have never looked back. My quilting is simple stuff - I'm color blind and quickly found out that quilts with a lot of different colors/fabrics confuse me and don't get finished. So I have a limit of about 4 fabrics per quilt. Added to that, I am impatient and want to get the quilts done quickly. I make lots of donation quilts, and grands and my kids are all recipients of quilts.
But it really boils down to the fact that I love fabric. And need an excuse to buy it.