Why do we buy compost?

I made all my own this year with coir, soil, perlite, sand, fertiliser, homemade compost, leafmould, etc. I started off being meticulous about the various recipes but after a while just chucked in what was available, reclaimed compost, manure and stuff until it felt right. It was very satisfying stirring up a batch in the wheelbarrow. I can't say I noticed any difference between my own or bought. I might have used a last year's bag of bought for early sowing but not sure. I'm going to miss Wilko for getting coir.