I assume the reasons why people don't play ToS as much as they used are:
1) melee is generally favoured these days, mostly due to PvP changes
2) ToS have aggro issues in PvE when outputting sufficiently high DPS due to the AoE nature of the class
3) 2 is largely a learn to play issue, but many people cannot be bothered I guess
4) BS and PoM favoured in PvP, and this trickles into the PvE side (why play 2 classes when you can get away with 1)
I love my ToS though. It's still my favourite class.