Just about all other electronics get cheaper over time but the cameras prices just seem to keep going up.
First of all cheaper is a really misleading term. Cheap doesn't infer value at all. If cheap were the criteria that governed all our purchases we'd all be using generic products and would only purchase the least costly tvs, computers, software, cars, homes, food, etc. I doubt you do that.
I don't believe that cheap is the case for any electronics other than commodity items. Most of the reduction in price for those are based on longer term volume and recovery of capital costs of manufacture.
I don't think DSLRs or mirrorless cameras can be considered commodity items. In the markets that aren't commodity items you generally see price points or tiers that exist. What that means is that you get more or better features with new models rather than lower prices. This is exactly what we're seeing with the A7r to A7R II progression. Competition enters into pricing also. Sony obviously wants into the market in a big way and is willing at this point to accept lower profit margins to gain volume and market share not to mention mind share over Nikon, Canon, et al.