Just HP stacking on enemies doesn't equate to an increase in difficulty

[Kalise]

Why to companies think that making a HP sponge being able to soak even more damage equates to an increse in difficulty?

Technically, it does.

More time spent killing stuff = more chances to fail mechanics.

Hard to mess up mechanics if you don't see them 'cause you zerged through the fight in 0.1s.

That and it gives a sense of difficulty without actually making things mechanically difficult, so that horribad players don't get butthurt when they fail constantly. They just think "Look at how good I am, I defeated this difficult boss that took like 3 hours to beat!"