I have spent a lot of years pondering this exact thing before I was diagnosed. Most NTs are liars and manipulators and I don’t know or understand why at all. This is just their accepted way to be for some reason. For relationships they pretend to have similar interests and beliefs until they think they have a good hold on you and then start to show their true selves after they have reeled you in. At that point they try to mold you into what they really want, whether you accept it or not.
Personally I have always found that entire concept completely illogical and counterproductive because it’s all based in lies and manipulation, but there you go. I would tell people (in both relationships and friendships) that they have to accept me the way I am or keep looking elsewhere. To quote the great philosopher Popeye “I yam what I yam an dats what I am”. But the Norms (“normal” people or NTs as many Aspies call them) like their games and rituals and perform the manipulation tactics anyway. I unfortunately wasted a lot of years with some really crummy women and so called friends because of this, and then avoided relationships for many more years after because I couldn’t figure out what I was doing wrong. I knew it was my issue because relationships seemed to just sort of work for other people, or at least for a lot of other people I knew. Now I am getting a better grasp of why.