My greenhouse gets much more sun on one side than the other. Some plants appear to be more light sensitive than others, so I do turn mine, but not on any form of regular basis, only when I see that the plant is inclined towards the sunnier side.
In habitat, as you say, they are fixed in position, so you do see plants that have grown towards the sunnier direction, but then the sun generally is very much stronger than we get here in England at least, so it can be less marked.
I don't think it inhibits the flowering as far as I can tell. In habitat, many Mammillarias grow in part shade, under trees, or other spiny bushes, or in grass, and so don't need all day sun.
Tam is right, it takes a while for plants bought elsewhere to become acclimatised to your own specific conditions, just as they will take a while to become used to your watering regime and your own preferred potting medium.