Which GM are you talking about? You might want to do this. Nothing in the Moldvay Basic rules implies that a GM might do tjhis.
So are you exhibiting selective memory and you have just "forgotten" the portion of Moldvay Basic that I quoted that does in fact imply that there are adventures above ground? I'll help you recover your memory by posting it again.
"It is the DM's job to prepare the setting for each adventure before the game begins. This setting is called a dungeon since
most adventures take place in underground caverns or stone rooms beneath old ruins or castles."
Those two sentences make it a fact that in Moldvay Basic, not all adventures are in underground places and in ruins. That means that some are in other places like forests, towns and cities. Moldvay Basic just doesn't give the DM the tools to create those adventures. It's focus is on the typical dungeon.
Below are more quotes(not an exhaustive list) from Moldvay Basic that shows a world outside of the dungeon, some specifically mentioning taverns and one that lists towns as a place to adventure.
"Elves are slender, graceful demi-humans with delicate features andslightly pointed ears. They are 5 to 5'2" feet tall and weigh about120 pounds. They can be dangerous opponents, able to fight withany weapon and use magic spells as well, but
prefer to spend theirtime feasting and frolicking in wooded glades. They rarely visit thecities of men. Elves are fascinated by magic and never grow tired ofcollecting spells and magic items, especially if the items are beautifullycrafted."
"HIRING: To hire a retainer, a character must first find NPCs whoare interested in the job.
Characters will have to go somewherethey might find and interview interested NPCs, such as a tavern orthey must pay a fee to advertise for NPCs to come and see them."
"Acolytes are 1st level NPC clerics
on a pilgrimage to or from a holy(or unholy) shrine — or perhaps merely seeking adventure."
I love this one. Talk your way out of the bolded portion here, "Bandits are NPC thieves who have joined together for the purposeof robbing others. Bandits will act as normal humans in order tosurprise their intended victims. Treasure Type (A) is only foundwhen bandits are encountered
in the wilderness in their lair."
"Black bears have black fur and stand about 6' tall.They are omnivorous (will eat almost anything), but prefer rootsand berries. A black bear will not usually attack unless it is corneredand cannot escape. Adult black bears will fight to the death to protecttheir young.
They have been known to raid camps, seekingfood. They are especially fond of such treats as fresh fish andsweets."
"Grizzly bears have silver-tipped brown or reddishbrown fur, and stand about 9' tall. They are fond of meat and aremuch more likely to attack than black bears.
Grizzlies are found inmost climates, but are most common in mountains and forests."
"
Wild boars generally prefer forested areas, but can be found nearlyeverywhere. They are omnivorous (eating almost anything), andhave extremely nasty tempers when disturbed."
"
The party is hired to map unknownterritory. The area might once have been familiar butis now overrun or destroyed; a strange tower might mysteriouslyappear overnight in a familiar area."
"To remove a curse or recover asacred item, the
players must travel to a shrine which hasbeen lost for ages. The characters usually have only a roughidea of its location. The players may have to consult anoracle or seer during their visit."
Kings hang out at the entrance to dungeons with quest signs do they? "This is a scenario in which a
king (orother NPC) provides a reason for adventuring."
"It is not necessary to draw a detailed map of the dungeon first, butit is useful to have a general idea of what it will look like. When decidingon the shape of the dungeon, the DM should also outlineideas for rooms or areas in the dungeon. A few common settingsinclude:1. Castle or tower 4. Crypt or tomb2. Caves or cavern 5. Ancient temple3. Abandoned mine 6. Stronghold or
town"
At this point I've proven that Moldvay Basic expects the game to take place outside of the classic dungeon as it mentions going to taverns and plenty of outdoor regions and creatures for those outdoor adventures the DM creates. If you want to claim that Moldvay Basic focuses on the underground adventure, I'll agree with you. If you want to continue to claim that it's only about underground adventures, you will be continue to be wrong. Up to you.