Some DM's were world builders early on, creating complex game worlds full of lore and things to explore, but it's true, most of us were just running adventures and seeing what would stick. PC's had a high rate of attrition, and at least in 2e, it took forever for players to level up if you were keeping meticulous track of xp- I know of several DM's (including myself) who basically had milestone leveling before there was a term for it, advancing characters when it felt appropriate. It wasn't ideal, since it short shrifts characters who advanced more quickly, and advancement was now at the whims of the DM, but no one was really happy with xp from monster kills either.
The DMG would talk about story awards, but not actually give you much in the way of guidelines, and class xp awards were 1) optional, and 2) required close record keeping and could have lopsided results when Thieves were getting xp for treasure, Fighters were getting bonus xp for killing stuff, and Wizards were getting bonus xp casting their very limited spells, lol.