It seems like most of the celebrated OSR games leave out the exploration rules/procedures that were IMHO the core of old-school play. Even games that are billed as continuations of Gygaxian D&D, like Castles & Crusades and Hyperborea. I'm referring to things like dungeon exploration turns and wilderness exploration procedures/hexcrawl rules specifically.
Why do you think these rules get left out so often?
Some games like Hyberborea have different concerns. For 'dungeon fantasy' games like C&C I think it's a genuine failure to appreciate their importance to the core gameplay loop.
It seems like something that should be included as part of the most basic part of the rules is "how to build a dungeon".
I think this is partly why Moldvay's rules are so popular: they give step-by-step instructions for creating and stocking dungeons, plus an example of someone building a dungeon.