There is a really interesting debate going online right now about whether the rate of improvement in America and the west in general has slowed. The debate has been started by a book by Tyler Cowen called "the great stagnation" which I have yet to read.
Above is a graph from here of how quickly different products became popular
Paul Krugman raises a similar point about how American Kitchens have not improved much from the 1950's here where he points out "By any reasonable standard, the change in how America lived between 1918 and 1957 was immensely greater than the change between 1957 and the present."
You could argue that kitchen equipment is much cheaper than they were in the 1950's. Or that rice cookers, food processors and microwaves are a great improvement. Coffee machines are probably the exception to the stagnation rule as they do seem to have improved vastly. There is also the explanation that if your home kitchen has not improved maybe the kitchen that cooks your food has.
Has the big change been that people do not use their kitchens anymore? In a 1950's kitchen could you order a pizza to be delivered? Dominos started in 1960 according to the history of pizza delivery here so you probably could. I doubt Italian, Chinese, Mexican and Indian food were regularly delivered to ordinary peoples homes though.
Has the technology and labour moved from the domestic kitchen into industrial kitchens that now do 90+% of the work in preparing many of our meals? How much of the supposed lack of improvement could be explained in terms of more processing happening outside the home?
“About 44 percent of food dollars are spent outside the home – a figure that started rising sharply in the 1970s, as more women joined the work force. Full-service restaurant revenue rose 5 to 7 percent a year in the decade leading up to the Great Recession”. So do seem to be eating out more?
Houses with small numbers of people cook less. And houses have less people nowadays, due to demographics. If people eat out more (or order in). Why would they buy some brand new kitchen invention? I have seen people with kitchens filled with shiny new equipment they have never used but I think this is fairly rare.
If the dial up pizza restaurant can have a new dough maker that is more efficient it makes sense for them. I can ring them up now and get the use of their new industrial standard food technology for the minute it takes them to make my pizza. Maybe home technology stagnated and the restaurant/supermarket/Microwave dinner technology improved?
I think it is worth noting that the improvements in Irish kitchens in this time have been huge. The 1918 world Krugman describes is superior to my grandmothers life in the mid fifties rural Ireland. She did not have running water or electricity and in her lifetime between 1950 and 1980 the changes she saw were massive.