Because back in the day, relics were used to revive older content, incentivicing players to unlock and do it.
I'm tired of seeing Crystal Tower in alliance roulettes and The Fist of the Father or even worse - the Cuff of the Father - in my normal raid roulettes.

But besides that, normally I only go for a single relic. I was looking forward to a long term goal, then I got my relic with 0 effort, because I was already capped on tomestones.