To us they seem like non-count nouns for naming types of stuff.
But of course, to enforce it you have to be able to distinguish count from non-count nouns.
The Danish philologist Otto Jespersen expounded the concept of count and non-count nouns in an unpublished lecture to the Copenhagen Academy of Sciences in 1911.
Lot here is not used in any literal sense; it's what's called a non-count number-transparent quantificational noun.
Now, vanity is a non-count noun, only very rarely used in the plural.