Enemy mob health bars in PvE
Yeah and in the end you have a number there nobody can read anymore. Also it is rather easy to predict the percentage of the health of a boss quite precisely, no need for that.
There are issues and development choices that went into that.
First off, the issues. With a percentage, you end up trivializing certain boss mechanics, which trigger at specific health amounts by giving out all the information needed. On the other hand, giving away boss HP would probably result in every more rage about condition damage being inferior to direct damage.
Second off, I recall some dev post in some context mentioning that one of the goals of obscuring the HP is to simply make sure the player focuses on the game and not the UI.