It's seen as a fad because of the large initial water weight loss and the numerous myths about it, e.g.:
1) it's impossible to gain weight while in ketosis
2) the first time you go into ketosis, it has magical fat-burning effects that are lost after you go out of ketosis and back in
3) that ketosis is in fact magical in any way, and in any way better than simply -moderating- carb intake (as opposed to cutting it to 50g or under, and giving up delicious things that you enjoy).
Fact is, plenty of people have tried it as a magic bullet and eaten copious amounts of cheese and bacon only to find that, surprise, fats are insanely calorie-dense and things like salt can still happily make you hungry enough to overeat.
On the positive side, trying keto also permanently changed the way I felt about food - I permanently reduced my carb intake, increased protein and fat, and have a much better understanding of how high-carb foods create 'hunger'. And it happens to work very well for some people, which is awesome.