I think it has a lot to do with how common they are, or rather aren't. I see diesels almost every day, lowly 156s and 158s or big old 66s and 60s, fast HSTs or horrible old pacers. Aside from the 225 and the frankly bogging 321 and 333 I don't see any, so can't get too attached to them. I do have a soft spot for the 92 but have only seen 3.
I must admit to only really being interested in steam or modern diesels, I run a 156, 66 and a 67 on my Scottish layout (as well as some special steam in the form of the Jacobite).