I spent 30+ years as a manufacturing engineer in the electronics industry. Many consumers would be surprised or shocked to learn how many features or options in an item are deleted (or added) due to the effect they have on the cost of the product either in parts cost or manufacturing costs.

While marketing people often push the envelope to include wonderful "whiz-bang" features, if the parts costs or the costs to implement these features exceed certain set points, the accountants will veto those features. Unless it can be proven through market research that a feature is going to significantly increase the sales volume of that unit and pay for the increased in-house costs, it is usually a no-go.

It is my belief that manufacturing and development costs were the big drivers in the mirrorless market. Eliminating the mechanical mirror in the Dslr probably reduced the parts and manufacturing costs significantly while adding the ability to shift much of the development costs to software-driven improvements. Removing mechanical parts also improves reliability and lowers repair and warranty costs.