Raids dont experience alot of traffic because most of them drop loot that either is invalidated by power creep or is niche/TR twink gear at best.
In the first 2 years of this game we had 9 raids. Every single one of those was run quite a bit, because most of that loot still mattered.
Since raids are the last bastion of having artificial time barriers limiting how many times they can be run, if the loot isnt worth it, people dont run it. They also wont spend money on timer bypass to run a raid where the loot is long obsolete.