The Herculean alike Fighter or Ullyses Warlord scans the scene after noticing the party is in a broadly bloodied and losing. Notices with his Engineering Skill a flaw in the structure that will do nicely he hurls the hammer just so and gets lucky in the manner high hit point and well levelled characters often do and collapses the roof when the dust settles the Hoard of ravenous berserker trolls that was over running them are cut off from the party
Yeah, that'll never happen. You've gotta 'plan for it,' which means loading up on the right spells/items...
and muttering something in a strange tongue about their lunch committing suicide.
"...I'm not hungry enough to dig up the bodies, maybe later... do we have any halfling left from yesterday? We have some troglodyte... hasn't that gone bad yet? ...no, if it does, it'll start to smell
good..."
Each scenario and situation is different, which is why it's important to plan these things. Or at least, it should be. There are character builds, spells and magic items that boost movement rate and increase carrying capacity. There are items that can be used to slow or confuse pursuers. There are tactical options, skill challenges, etc. that can be used to distract, delay, or de-escalate.
That's getting into another thing that it seems hard to get D&D characters to do: coordinate. I mean, focus-fire is
just within most adventuring cat-herds' tolerance, but coordinating
builds?
The options are there, and they are largely ignored by the players (and the DM). I don't think the game is the problem.
Oh, if there's a problem with the game, the game's likely part of the problem. It might not always be the whole story, but it's probably in there somewhere.
For instance, it seems plausible that before they get sophisticated enough to do the kind of magic-item-allocation planning you're talking about, let alone build coordination, a group could have probably had at least one TPK where they tried to get away and couldn't, because the monsters were just faster than them, or they didn't leave the slowest PC behind (or they did, and subsequently TPKd for want of healing, because he was the cleric), and also experiences where they
thought they were all going to die, but, thanks to lack of death spiral mechanics* (and maybe the DM fudging some die rolls or hp totals behind the screen), pulled through afterall.
In other words, not running a way is something they learned from how the game played. So, even, now, in 5e, when they have a pursuit sub-system tucked away in the DMG, they're not likely to give you reason to look it up.
* of course, death spiral mechanics will
also hurt you when trying to run away, so no help there, either.