The 5 Love Languages is not supported by any scientific research, basically, it's a load of bollocks. It's just the latest self help book to be in vogue.
Lots of things that work aren't supported by scientific research (yet?). It's your choice not to use it, but to claim that something is bollocks probably means that you will never follow what most people tell you about lots of things (where are all the double-blind peer-reviewed studies about how to bake a good cake or write a good novel?).
Yes, but claims about a "good cake" are not making generalized claims about human behavior. The only downside of a "bad cake" recipe is someone trying it and it's not a great cake.
There are massive consequences for releasing a book claiming to be a factual model for how human brains work and how people should behave towards each other based on this model. If the book becomes popular, this sort of model can become the defacto truth to most people and live on in public consciousness for years as pop psychology.
As an example, look at things like Meiers Briggs (ISTP, ENFJ etc), "Type A vs Type B personalities", DISC personality testing, etc. ALl of these are based on old, flawed, and straight up bad research. Yet companies across America (and the world) are still giving people training and hiring people based on these studies. Note, DISC, for example was based on William Moulton Marston's work, a guy who DIED in 1947. The "research" which became DISC is from 1928! Businesses are still dressing up this old and flawed research and selling it to businesses for huge profits.
