I find your GMing weird and dysfunctional. I certainly wouldn't want to play in your game.
I run my games (mechanically) according to the recommendations in the DMG (average adventuring day features 6-8 encounters, and around 2-3 short rests).
I also impose time limits on my quests. Examples include:
1) Stop the BBEG from completing the ritual by midnight or else CR (lots) demon is released into the world.
2) Rescue NPC from lizardfolk before she geats eaten in the victory ceremony.
3) Escape from the dungeon before the boat leaves in 3 days time, marooning you on the island
4) Save the children captured by the Kobolds before they get sacrificed
5) Recover the artifact for NPC before rival adventurers recover it
6) The evil archmage returns to the dungeon in 4 hours. Recover the three items before then or else you become his prisoners!
7) The town is beset by a plague. Locate a cure within 3 days and you get paid a bonus; dozens of townsfolk die daily.
etc etc
In my games, I police the adventuring day a part of quest and encounter design. Its part of the job of being a DM - to frame the quest/ adventure/ mission within a narrative the players can explore. My players know the
objective, they know how much
time they have to complete it, and they know the
consequences for failure.
Within that framework they attempt to complete the quest (rescue the NPC, stop the ritual, escape the dungeon, find a cure. save the children etc) within the allotted time, conserving resources to achieve the end goal. Going Nova on encounter 1 will make encounters 2-7 much harder.
Encounters in 5E are not the ends in and of themselves. They are a smaller chunk of a larger puzzle (the adventuring day/quest).
IME PCs seek to retire whenever they are significantly below full resources. That's true in every edition.
Of course they do. But its your job as DM to ensure that they most often cant.
You should be structuring your quests (these are simple dungeon hacks, but the same applies to every quest) along the lines of :
'The PCs need to locate and destroy the BBEG by midnight to stop his evil ritual, and he's in a typical dungeon, populated by 6-8 [medium-hard] encounters, and its currently 9pm (giving them enough time for 2 short rests, and an hour of adventuring)'.
'The PCs need to locate a macguffin for their NPC patron so he can present it to the King on his coronation, 3 days hence (3 level dungeon with around 6 encounters per level)'
If the PCs nova encounter 1, good on them. They now have no resources left to complete the quest. They fall back to rest, they fail (and incur narrative consequences). On a standard/ default 6-8 encoutner adventuring day they are required to marshal rand manage resources over the entire quest/ adventuring day, instead of a the boredom of managing resources over a single encounter.
It's very poor GMing to impose the same artificial "you must complete 6-8 fights before resting" paradigm in every session, every adventure, and every campaign.
I absolutely agree, and
no-one is suggesting you force every adventuring day into having 6-8 encounters and 2-3 short rests.
You should be aiming for round 50 percent strike rate (enough so the players self regulate resource usage). At that frequency the players will naturally self regulate and adjust to the expectation that they are more likely than not going to get several more encounters before being allowed to long rest. They will hold back on Nova strikes, as they never know when another encounter is around the corner. Also; at that frequency nova 'builds' wont occur at the table. Characters will be built for marathons (built to be effective for 6 encounter/ 2 short rest days), not built for 1-2 round bursts of damage (the assassin 3/ fighter 2/ paladin 2/ sorcerer Nova builds).
Most days* will feature around half a dozen encounters, and opportunity for 2 or so short rests.
Some days* will be one or two encounter days (where long rest dependent classes like Wizards, Paladins and Barbs will shine).
Some days* will feature several encounters in waves, with little chance to rest at all, favoring rogues and champion fighters.
Some days* will feature a half dozen or so encounters, and plenty of short rests (one after every encounter that day) giving Monks, Warlocks and Fighters the chance to shine.
*'Day' in this context meaning [the time between long rest resource recharge]. It can be any period of time you as DM desire.
Also; I note youre conflating 'session' with 'long rest'. They are not the same thing. Get used to players long resting only every second or third session. Your game will be better for it.