In the game, most if not all open world areas are for solo game, how many of these areas are there? that's well over half of the game content. There are also several dungeons for solo play.

There are many occasions in PVE alone when a PoM got targetted in melee (obviously this is the norm in solo play, and even in group or raid it still happens to take aggro when going full out and depending of the tanks). In PVP no doubt they are too.

Active blocking makes sense for me after a double tap back while waiting for the few seconds of timer resets and for many other situations.