We assume that technology will get more efficient in many things. Why would stone cutting be one area where technological development has reached it's peak and humanity can never have so efficient rock handling and cutting that making some walls from rock blocks would be cheaper than making them from concrete?

Making a stone block requires destruction of thin slivers of rock. Currently, that usually means that a circular saw turns that sliver into dust. Those saws often contain very expensive and hard materials so that they last longer. There has to be balance between price and hardness. For example, if some material is 10 times softer but 20 times cheaper plus the replacing of those spare parts is automated and fast enough, it may get cheaper as a whole.

If the blade is 100% metal (not with diamond tips or some special ceramic), there is a possibility that the work site could have automated device that heats and forges the outer edge again to be a sharp blade. Radius of the blade decreases every time, unless more metal is added on the edge.

Stone dust and atoms from the blade get washed away with water. If some of the chemical elements in the blade are costly enough, the waste water can be filtered to get them back.

With many building projects, there are bumps of Earth crust with inconvenient shapes on the way, that have to be removed anyway. Usually that is done by drilling holes for explosives, with all the trickiness that comes with explosives. Then the rock turns to pieces with random shapes and sizes. In some places, there instead maybe could be 10 rock cutting blades working in parallel to turn the obstructing rock into elongated cubes. Also, some room walls may be formed by leaving long flat pieces of rock untouched when getting stone blocks, so that these walls would be continuous and part of the original rock.

More automation can reduce prices and some of that automation can be such that it adapts it's actions to the situation instead of going with pre-programmed trajectories: for example, 3d scanning rock with cameras, lasers and ultrasound and then planning optimal cut directions.

Also for cutting random shaped pieces of rock that are already separate from Earth, so they fit together in a wall.

Some of these methods could work in Moon and Mars too. Blade has to move slowly to avoid overheating or pieces have to be moved to a pressurized volume so that water can be used. Using water cooling outdoors in Mars would be very tricky.

Optimizing rock piece fitting may be the kind of computation that would get some advantage or benefit from quantum computers (if they can work)?

In some places, random rock pieces can be cut in only 4 sides to make a tight wall, when 2 sides remain random. Cutting just 2 sides can enable some stacking. Random shapes reduce echoes.

Somewhere around 60 or 100 years ago stone use plummeted, apparently because making concrete became cheaper.

When rock and concrete pieces have the same size and shape, rock has better chance of being cheaper when the size is bigger, so there is more volume per cut surface. Thicker walls mean better sound proofing, thermal inertia and insulation. Most of the thermal insulation may come from some other material.

Most of the building would still be made of reinforced concrete, steel and / or wood. In some spots, maybe also random shape rock binded with concrete ( like medieval castles ) and gabion walls, but computer-optimized for tightness and assembled with automated machines.

Cheap enough rock blocks may not need science fictional technology, but let's consider what those could be:

Cutting with heat or acid.

Cutting with proton beams or ion beams, maybe helium nucleus or lithium nucleus. Mini-particle accelerator launches them.

New chemical elements from the island of stability, found from asteroid cores. Putting those on circular saws makes them super durable.