It's because this game is an MMORPG and that makes it DPS-oriented. People are obsessed with DPS so if they have to Esuna then they have lost their precious DPS uptime. The implementation was also poor in many cases, with the status effects lasting about as long as it would take to Esuna anyway. I thought about what might make someone Esuna and one of the things would be sleep, but in this game being attacked by the boss means sleep is interrupted anyway.

I thought about what would make healers actually heal and esuna a lot and I think combat speed is a big factor. If the GCD was changed to 10 or 20 seconds (as extreme as that sounds), and the rest of the time was just dodging mechanics, it would mean that you have to think more carefully about what you spend that rare GCD on. A heal? Or an attack? You won't get to use it again for 10 or 20 seconds. So it might make you heal.

That would make it more like traditional FF games, where because your attacks are much less frequent, you have to decide more carefully if they will use an attack or a heal.