Laminate requires an expansion gap. When installed without a gap, laminate buckles up as the flooring heats and expands. Leaving the gap exposed would be unsightly, so the floor trim should be installed over the laminate.
Tile likewise should have an expansion gap when installed over a dissimilar material, like wood subfloor. If the gap around the perimeter of the room is filled with grout, either there won't be sufficient room for expansion and the grout or tile will crack, or the title will contract and you'll be left with an unsightly gap.
Solid or engineered wood flooring can be installed over a subfloor floating (like laminate), nailed, or glued. When floating it requires an expansion gap for the same reasons as laminate. Even when nailed or glued, there's still a little thermal expansion happening. Walls are never exactly straight, and it's difficult to cut the flooring to fit just right without an unsightly gap. It's also difficult to apply a floor finish right up to the edge. So installing trim over the flooring edge is easier and looks better.
In contrast, carpet is stretched between tack strips. There's enough elasticity in the carpet to accommodate thermal changes and cutting inaccuracies (for normal-sized residential rooms, anyhow), so there's no need for an expansion gap, and the edge of the carpet pressed against the wall looks neat. Lacking any technical or aesthetic reason to have a gap, it's less labor intensive to simply leave the skirting in place.