Wdym why buy them yourself?

Because it's not a lot and I can?
With just pills I'd still have to click away for all my regular knuffels when I wanted to dig with them. I don't have as many as you do, but it would still be too much trouble. It's easier to have the apples and cupcakes just equipped in the knuffel rooms. That way the knuffels are always ready and digging takes me about 10-15 minutes then the apples and cupcakes restore the energy bars and so on.
I don't buy knuffels often, so it's no trouble to buy one more apple and cupcake when I get a new knuffel. As you said, they're quite affordable. I'm not as active anymore and don't have prosperous selling threads. I sometimes sell materials but most of them are free anyways (since they're not much effort for me to get them) and if they are paid the price is nowhere near the price of an apple or cupcake.
I don't sell items that much anymore. I don't even have the time or energy to keep up with my charity thread to give stuff away.
Why would I ask anybody to buy an apple or cupcake for me if I can buy them myself whenever I need?
The amount of materials I have doesn't bother me, I rarely look at the materials tab in the inventory. The avatar items I don't use bother me much more but as I said, no time or energy to put them up anywhere.