Because that's not the same as "The former members are not here."
(Btw, your sentence would be: "Burada eski üye yok.")
I am not sure but is it possible I anywhere read that "eski" meaning "old (in years)" was for things and "old (for persons)" was yasli. Is that right?
Yaşlı is the opposite of young, and eski is the opposite of new. People can be eski, objects can be yaşlı; anything can be either of them. When I say "eski karım", it means my ex-wife, not the current one. But if I say "yaşlı karım", it would mean "my wife who is at an old age."
I think "burda" is how "burada" often gets said in everyday speech, but that it technically isn't considered "correct," sort of like how I as an English speaker could say "I'm'nna do it after breakfast" perfectly happily but it wouldn't occur to me to write it down that way (I'd probably write "I'm going to do it after breakfast," or possibly "I'm gonna do it after breakfast," depending on how informal I wanted to be).