How does it not? The presence of gods, demons, devils, aberrations, fey, etc. all reveal that there exists worlds and realities beyond the mundane and familiar. An invisible world previously unknown is glimpsed by the existence of these creatures.
To a simple fisherman, learning the existence of an aboleth, a powerful aberration from the deep past, would fundamentally shift their worldview.
I feel like you're giving the impression that you're not really unfamiliar with actual D&D settings.
Can I ask: how long have you been playing D&D, and what settings have you played in?
Because in the FR, absolutely no, finding out about Aboleths is not going to "fundamentally shift the worldview" of a "simple fisherman" (also why are we centering things on "simple fishermen" in a setting which literacy is common, reading is common, education is relatively common, and so on?). They've likely seen dragons fly overhead, or at least manticores and wyverns. They've heard about countless monsters. They know about devils and demons and so on. They know about Drow. They're not a myth - they kidnapped their cousin and burned down his village. His wife's brother's uncle is a Tiefling. He talks to the Dragonborn who guards the gate to the town every morning.
Devils, demons, fey - these are not surprises to him. They are not mythology to him. They're very real things to be concerned about. Or utilized, or worked with. He knows they live in other dimensions, but that's not something he needs a god to "elevate his consciousness" about. It's just a fact. He doesn't want to go the Feywild. That adventurer who passed through town a few months back was from the Feywild and was a right handful and didn't make it sound like a whole lot of fun nor a very special place.
Even if the bloody Mists kidnapped him to Ravenloft, whilst he's probably never heard of it, he's likely to work out that he's been magically kidnapped and This Is Bad, and isn't going to have a new "worldview", because he's already familiar with the concept of people being kidnapped to other realms.
The same applies to Dragonlance.
The same applies to Greyhawk (for the most part - people are less educated but not quite the surprised simpletons you seem to want to centre).
Planescape, you literally are the extraplanar beings.
Spelljammer - see Planescape.
Birthright - Similar to FR/GH, maybe a little more peasant-y, but halflings, are from another dimension and can go there, so no-one is going to be surprised to hear other dimensions exist or have their minds blown by them.
Eberron - see Forgotten Realms.
Need I go on? What D&D setting are you thinking of where nobody knows jack and they need the gods and so on to "elevate their consciousness"? And can we stop trying to use "it would surprise literally the dumbest hick in the setting" as the bar here? Lantanese smokepowder would blow the mind of the dumbest hick in the FR.
