Kirby has stayed with its same basic design for over 90 years. Because it is the design that has always out performed others 95% of the time. Other companys changed thier designs to attract costomers. The machines didn't aways perform well. But that was ok as they would try something else. Few other Uprights have the performace of a Kirby. And most can't compete with its durability. At least other brands made after 1970.
We have plasic vacs for those who truly can not use such a heavy unit and those that think they can't push or operate a Kirby. The dispoasable vacuum gives the buyers many choices. Gives me the chance to laugh at all the gimics they fall for in a vacuum that can't compete with the Kirby. Any comparisons that are done are slanted in favor of the competition. With all the commercial vacuums available to me plus the domestic machines. I still Opt for my Kirby. It may not be the perfect vacuum in every situation but it serves me well in 99% of them.