Size and weight DO indeed matter. It may not matter to some, but to those that have arthritis, or other physical ailments that develop with age, what used to be a manageable camera and lens combination may not work any longer. So a lighter weight body and lighter equivalent lens is very welcome by many.
These may not matter to you or I that much, but I know many on the forum where this does, and even in my family, I have photographers where this matters more and more. My dad would be unable to carry around the gear I do, he would just give up photography if he had to. This is why Sony is still superior to Canon in regards to mirrorless, because their bodies are quite a bit smaller and lighter, and some of the equiv lenses are also lighter. This means Canon better care perhaps a bit more than maybe you or I do on this front, because otherwise, as folks get older, they will migrate off Canon gear if there are no options.
And this isn't just an age thing. For avid hikers, every pound removed from their gear means less fatigue farther down the trail. For frequent travelers (flights, etc), having lighter smaller gear means that there might be less carry-on or one fewer checked bag, and less weight to haul from the airport to the hotel to the various site destinations.
For some, I suspect weight/size is MUCH more important than Eye AF or full-frame AF capabilities or High ISO performance.