Bump old thread close old thread

[classic12]

Sometime i search on google or on this forum for a solution to a problem and you find that a person posted a thread about it so you interact with it without paying attention to the thread date.
this called bump old thread.
sometimes it don't matter if it's old or new since the problem is still there and the thread can help members that didn't seen it before
it's better than open new duplicate thread
even if the op is not still there but other members need it
than why old thread don't get closed automatically ?
and only one someone bump that thread again they close it.
why not all old thread are closed than