Part of this attitude probably stems from the Basic/Classic line of D&D. Either B/X or BECMI introduced Morale ratings in monster listings. People who started with Classic thus probably feel a little lost when exposed to OD&D, which expects GMs to decide on a case-by-case basis. The trick is that OD&D differentiates most monster morale behaviors not by a general rating, but by what each monster considers a "highly dangerous or un-nerving situation". Goblins, obviously, think sunlight is unnerving; cavemen think magic is unnerving; berserkers and minotaurs don't think much of anything is unnerving.
One thing I propose, to get something with slightly the same feel as Classic morale, is to not count any situation as "dangerous" for a monster unless:
- average opponent hit dice is more than their own, and
- number of opponents is equal or greater than the number of monsters; or,
- number of opponents is more than total hit dice on monster side.
Example 1: Ten orcs facing typical adventuring party. Even if the party is high level, orcs and monsters in general will go by the average hit dice of ordinary men: in other words, 1 hit die, same as the orcs themselves. Orcs will only make a morale roll if they are outnumbered by the party, or the party displays amazing firepower.
Example 2: Five ogres facing typical adventuring party. Ogres will only check morale if there are 20+ people in the party. If there are 17 members of the party, ogres will check morale after one of their number has been slain. If there are 9 members of the party, ogres will check morale after three ogres have died.