As already mentioned in the comments, cost is one of the primary reasons when you're looking at simple light microscopes. Inverted scopes have more complex optics, along with the convenience factor of being able to examine larger samples, generally having a more stable frame, etc. All this leads to higher cost.
An advantage I can think of for smaller upright scopes is the ability to use them as a dissecting scope, where the sample is opaque and you need to see it from above. Another advantage is this:
Many fluorescence microscopes are upright, as there is a significant amount of extra equipment that needs to be mounted in addition to the eyepiece, including lasers, stage motors, and cameras and other detectors. This can take up a lot of room, and for convenience's sake it's often easiest to mount it up top where it is accessible.