Hm probably several reasons.
1) I really was too thin before at one point, even by non-feederism standards.
2) It's easier to catch the attention of BBW (or other gainers), which is convenient.
3) I actually enjoy eating now, though only heavier foods. I'll still eat salad, but I need to use lots of dressing and ideally, bits of chicken and bacon. Ideally the dressing is something creamy, like Caesar.
4) The additional heft, thickness, and softness feels nice. Pretty sure I'll give better hugs as I gain more.
5) The heavier I get, the more I can eat, which helps me gain more. Although the pace and rate of gain hasn't been as fast as I might like.
6) I actually feel happier after gaining some, but I still need more.
That's just off the top of my head.
3 years