If you switch to Canon or Nikon, you will have wider selection of lenses from both Canon/Nikon and third-party makers like Sigma. Plus, you can use the same lenses for when you switch to a dSLR, if at all. OR, you can experiment with the larger forma...
The history of photography? Photographic technique? Critique of a given photographer? Review of photographic equipment? Darkroom technique? Film versus digital? Small format versus medium format versus large format? Canon versus Nikon? In other words...
They're the best product for the price. People become "loyal" to certain companies because they've grown accustomed to the brand. This is especially true of electronic and automobiles. Some people won't buy anything but Chevy, because of how it's mad...