The only problem is that the coffee they were consuming was freeze-dried and that's the taste they desired. The rich, deep taste of vac coffee was not to their liking. Vac pots are not as easy to clean as other types of brewing equipment. The thick, pasty grounds left in the upper chamber have to be wiped and washed completely, and of course this is not a factor with instant, and percolators are a bit easier to clean as well. With the post-war economy there was lots of manufacturing going on once the economy picked up, and in general, the speed of life increased.
Instant coffee is, well, instant- real fast.
Hot water, a couple of spoonfuls, and it's off to work. There was no place for a coffee maker that was the same as the one that grandma used. It was a matter of being different to be modern, not to be better, Even though the percolators made an inferior product, they looked sleek and modern, and that's what mattered when serving coffee to guests. Fortunately, vacuum brewing was not entirely abandoned. There are still a few manufacturers making vacuum pots.