language conventions are rarely conscious. they just happen. every now and then there's a campaign for our against using certain words or phrases; sometimes they stick and sometimes they don't. but those are conscious i guess. mostly though it just happens organically.

like a perfectly normal word becomes vulgar in time if enough people just say it a certain way. it's not like people suddenly hold a meeting and decide this word is bad now. it just starts to feel like it after a while, so it eventually becomes so.