"Assuming typical adventuring conditions and average luck, most adventuring parties can handle about six to eight medium or hard encounters in a day. If the adventure has more easy encounters, the adventurers can get through more. If it has more deadly encounters, they can handle fewer."
An average of 6-8 encounters a day has certainly not been my experience when playing 5e.
More like 1 or 2 encounters and then someone is calling for a short rest. In fact, how hard players "burn" through their short-rest abilities is determined entirely by the make-up of the group and the number of short rests a GM allows.
So, basically, Larian needs to enforce short/long rest type mechanics based on the pace that they want the game to be run at. They're the GM and should be using every tool in their tool kit to get the pace they're aiming for.
Terms like easy and hard encounters refer to the exp budget in DM book. They also suggest 2 short rests a day, less nerfs short rest based classes like warlock, more can make them OP.
When playing 5e I preferred being limited to one short rest a day. Principally because I prefer how earlier edition handle "resting" over 5e though... so I know I carry considerable bias.
Should they enforce this or let the players decide themselves(like baldurs gate)?
Different system so I don't think you can compare 5e to how a 2e based system did things. And if you just "let the players decide" they you're going to get different responses from different character classes (Warlocks and Fighters are going to want a bunch of short rests, other casters are not.) I'd rather not pit players against one another when it comes to stuff like this.
Off course should lower game difficulties get more rests(or maybe no restrictions at all)
I'd be onboard for that. More short rests do make the game considerably easier. In fact, I'd prefer these kinds of "difficulty settings" over just mathematically nerfing players and buffing monsters.
