EzekielRaiden
Follower of the Way
Before any direct answers, keep in mind the difference between "X is conceivable but not (currently) supported" and "X is simply impossible." James Gasik very clearly meant the former, given the explicit phrasing "there's no set way," so don't confuse their position for a much, much more strident one.Why is there no way for characters to learn about monsters? Why is retreating impossible? These are both common in my experience.
As for direct answers:
For the former, I find two major inhibiting factors. One, this places certain responsibilities on the DM which I find are often not handled well, especially for inexperienced DMs. That is, for any kind of "the DM needs to inform the players of X" stuff, many DMs struggle, especially since they are (sometimes perversely) resistant to ever just telling their players friggin' anything. It needs to be clear that there is worthwhile knowledge to obtain, and it needs to be reasonably accessible, and many DMs struggle with that (as do game designers of all stripes; it's easy to think a puzzle you wrote is very easy to solve!) Part of this is the paradox of ignorance: you need to know that you don't know something in order to start asking about it. You can't investigate or prepare for something if you don't even know that it's a possibility, and I find a lot of DMs struggle mightily with getting even enough information to the players that they can start asking. It's the stereotypical "you should have asked the one-armed man in the tavern!" "We talked with him, it didn't seem he had anything interesting to say..." "Well you should have asked him about X." "...we had no idea X even existed at that point!" debacle.
The second problem for this "why is there no way for characters to learn" problem is, if there's no current support, the DM has to invent it on the fly. And "the DM has to invent it on the fly" is what leads to tons of janky, inconsistent methods and subsystems floating around. It's why the early-edition DMG was such a nightmarish mishmash of stuff with almost no organization--bursting at the seams with useful tools, but those tools were scattered about like leaves. Gygax was very good at improvising, but very bad at editing and revising. It's not that anything is strictly impossible with D&D, it's that inventing consistent, well-designed, functional systems or group policies is hard and a lot of DMs are simply not very good at doing that.
For the latter: Again, less a matter of "impossible" and more a matter of "impractical" or "mathematically unfeasible." Many of the things that have good resistances can move faster than regular characters can. Especially if any of them are dwarves, halflings, gnomes, etc. The risk of eating an opportunity attack, or still being within range of any ranged attacks, makes retreat often unpalatable at best--and since the only reliable way to try to figure out how to break something's resistance is to try to break it with various things, players will often feel already committed to trying to do something, doubly so if most of the party is melee characters....who are, notably, the most punished by this sort of thing (since melee attackers usually rely on many smaller-size attacks, rather than single big hits, which are usually the domain of magic...and magic has the easiest time breaking through enemy resistance!)