There is no limitation on the magnification ratio per se. It is mostly a matter of making compromises and of manufacturing tolerances. In a 1-something scope you have to make sure the exit pupil at 1x is large and reasonably free of distortion. That is one of the compromises.
Then you have to mind the depth of field. The higher the erector ratio the higher the ratio in physical sizes of the image between front and rear focal planes. Since there is an upper limit due to how much space you have, if you want to increase that ratio, you have to make the reticle cell size in the FFP smaller and the focal length of the objective lens system smaller. If you do that, you may need side focus (think March 1-10x and 1-8x) since short focal length means shallow depth of focus. Then, if the reticle cell is smaller, the lines in the reticle have to be made thinner to look the same in the image.
As technology moves on, all of these things are more and more doable, but there are still compromises involved.
ILya