[great_kraken]

It flies in the face of modern food culture, and it's a difficult decision socially. I think this drives a lot of people. That, and they're unable to remove their associations of "how normal people eat" and they feel a lust to consume sugars / complex carbohydrates again. However, the ones that don't start eating more have much better results long-term. You can't get fat again if you don't go back to eating that which got you fat in the first place.

[DrScump]

  it's a difficult decision socially

This derails a number of people. Eating keto often means eating separate foods altogether from your family/peers, and your choices when eating out become limited and/or disproportionately expensive[0]. It also means that you are often put in a role of educating people (or trying to) about what you are doing, and why, and that can also mean overcoming skeptics.

Generally, however, after a few months of showing continued positive results, the skepticism turns more to curiosity... and you find people coming to you for dietary advice and reference material.

[0] some restaurants will work with you on this, and it never hurts to ask. For example, I've eaten at multiple diners where they would make a larger omelet in lieu of potatoes and toast.