It really seems like something that doesn't concern most fighters. Back in the day when someone latched on to a leg I saw a lot of panic. Now it seems nobody sweats them. I thought it was a result of fighters just understanding how to defend them better but your assertion is its a lack of fighters knowing how to apply them? Interesting. Very interesting. Thank you for your response.
Hmm, I think a lot of fighters know the basics in how to defend them, and so when facing a person who isn't particularly skilled they don't need to panic. Most of them know the basics at least, and if they are facing an opponent who they know utilizes leg locks they can specifically train for them.
I can't speak for the period you are referring to, because I wasn't watching then.
The UFC has a lot of semi-traditional grapplers, and as you mentioned, a lot of them don't like going for leg locks. It seems to be a Brazilian thing, although not all of them have a problem with it.
The other thing is modern submission grappling has a far larger audience than it used to, and it is now possible to make a living off it. Previously, you often had to go into MMA to make any money.
Nowadays, they don't need to transition, and so you aren't seeing as many high level transitions I think. Also a lot of them have realized that they don't have the wrestling to back up their submissions, after seeing many great grapplers get destroyed by people with decent wrestling and good standup.
I am straying away from going into technique, because as I say I only know the basics. I would say though that I don't see many people attacking the legs, I can't remember the last time I saw someone sit back into a 50/50. Maybe Cyril Gane? Anyway, I think that shows how little they are used, and the only conclusion I can draw from that is that people don't know how to properly go for them, also people know how to defend them better, and as such it is riskier to go for them.
Edit: Also as
@BRASIL WAND says, the positioning often leaves you very open to strikes, however there are definitely some positions that are less dangerous than others, and I think with more time we will see them utilized more in MMA.