Yeah I'd say realistically the only people getting into Castrum are those who just want the completion to get into DR.
The loathsome memories farming was made pointless through Crystal Tower raids, and generally i'd only step into Bozja to see if Castrum would pop but find CT runs more time effecient.
Add on that POTD is the better memory farming step for the part right after and Bozja is currently eh until the new area opens up which will hopefully help the CT raid step.
I haven't farmed a relic weapon in a month but people don't want to do Castrum anymore? I thought it was faster since it gave 5 instead of 1. Also PotD is better now? Did they increase the drop rate there? They did mention they will nerf the steps once the final relic steps come with Bozja.