I believe "cafe" means to severely reduce the overall utility of a bike.
It is less comfortable to ride, almost torturous for long distances.
Riding in rain is way more miserable, if even possible.
The "cafe" bike generally becomes more "special purpose", which is perceived as out of the ordinary and appeals to the "extreme anything" crowd in an effort to set them apart from the routine many of them have in life, and "one up" others in their peer group. The "cafe" bike's special purpose is often simply a fashion statement. Owning one implies mechanic and engineering skill, without the bother of actually learning those skills.
The "cafe" is a very short distance travel machine with almost no way to carry items needed for an overnight stay away from base garage, not to mention cross country travel, without a support vehicle of some kind.
It is very seldom tested for actual performance increase in any operating regime. The facade of a limited use "racer" is the driving goal and major sales point of "cafe".
"Cafe" also implies loner status as passengers are in no way accommodated.
I also agree that "cafe" is the current generation customizing bikes in a distinctly stylish way as the prior generation customized their bikes into "choppers". But, the style is distinctly different for the current generation to call their own.
For the record, I have seen some very nice customized bikes "cafe" and otherwise. Seen a lot of posers, too.
But, in today's marketing/advertising pervasive world, the value is in the label. "Cafe" is a label that sells in these times. IMO
Cheers,