I'm looking at it from the standpoint of the company. If I(the company) expect 6-8 encounters and an ability works just fine for 6-8 encounters, I really have no cause to change it, even if it wasn't intended. And especially if it makes it harder for those who want to try and alter the game to make it more enjoyable for their playstyle of fewer encounters.
I'm not actually advocating it personally.
I don't really see how that's possible without a complete redesign of classes, subclasses, spells, monsters and the combat math. All of that(and likely more) is based on resource consumption over 6-8 encounters. I'd love to be wrong about this, but I really don't think I am. Especially if they want even a tenuous ability to claim backwards compatibility. If they did overhaul everything that way, nothing from 5e would be even remotely compatible, having been designed for 6-8 combat encounters.