I've been thinking about posting this for a while, Doing it now in the hope the it prompts a new fresh WoTLK server.
My theory is the following: The player base was split across 3 servers gradually throughout last year – each convincing each other it was a dead realm, with realms masking their actual playerbase and a lack of trust in the figures, These servers start to bleed players who think their server is dead and creates lots of refugees. I believe the next WoTLK fresh server to launch with a higher exp rate than x1 with thrive. If your server already has a reputation unfortunately I doubt it would pick up traction and should consider restarting/repackaging the server.
Warmane TBC exceeded expectations, Angrathar decided to try and cash in and release their own TBC Server, Their 5k average players on angrathar was then split and the realm felt light and towns were emptied because people had jumped ship to the TBC server, During this time Dragonblight released WoTLK, The people who thought/seemed Angrathar had died jumped ship to Dragonblight leaving Sunwell with a low pop WoTLK and declining TBC server. The TBC server died and people moved back to angrathar which was now barren.
People then started to leave Dragonblight due to the lack of support with increase exp rates and very very late sorting out of their GM staff and moved back to Sunwell-angrathar which had consistently bled players whilst Dragonblight also slowly died. This and the fact that angrathar is a complete server with all content released.
This was my experience and impressions anyway. I do truely believe that there are a lot of WOTLK refugees who scan this reddit waiting for a fresh launch. I hope I am correct.