Because it would be helpful if Elsa keeps empathizing with humans and behaving in manners they consider acceptable. Mentally alienating herself is not going to help with that.
Youre making alot of assumptions there.
That Elsa will lose any and all empathy with the realisation shes not human (although seeing how Humans treat almost everything else I can understand that one), again there no actual indication this will happen, and seeing as I doubt Elsa will suddenly lose all feeling for her family I heavily doubt it will ever happen completely or to an extent that shes isolated. Hell her family dont act very human/normal alot of the time anyway, Elsa would need to change in a drastic way to stand out too much there.
That if she does lose her empathy she will go around alienating other peope and herself, which seems lie a bit if a jump. Alot of people have very different view points. You dont even realise alot of the time since they dont bring these things up and if they do its once youre close and can accept these things. Theres not much difference here. Unless youre afraid that Elsa suddenly gains some tentacles or outer mutation that will let everyone know shes accepted shes not human at all (and rememeber that we already know difimitely that there are other species in this world, do you think they are all completely devoid of empathy and personality?).
And finally a last assumption is that Elsa even needs the same kind of social interactions as (most) humans do or that it would afffect her in negative ways to have different ones. She could be one of those people who simply prefers her family to others, or one of those people who prefers not to get involved with too many people. Neither is a bad thing. And we have plenty of people like that ourself in our world.
Plus with a Royal Family like ours whos going to notice and complain abiut these oddities? Because I think ifthey would complain they would already be doing so. Anna and Mother arent the most normal of people.
... and as a last thought, with so many different races out there who's to say that Elsa cant find compantionship ith them? That forcing herself to think like a human even thiugh she isnt one migh not be so helpful when shes both not one and lives in a world consisting of more.
Tbh I also just like the idea as a whole. So obviously I'm biased. Still, like you I'm entitled to my opinion and vote. And I really think this acceptance is the ealtier route for Elsa ans one of the more interesting choices for the quest as a whole. We/Elsa cant keep pretending to be something we're not forever. And it will only hurt us if we keep putting this off for further and further down the line when we have less chances to adopt and learn about ourself.
Sry for the massive amount of text. I just kind started writing and didn't realise it was anywhere near this long. I'll try to keep things rather concise if I need to say somehting again. I just find the forum medium makes me much more verbose than usual as it kind of encourages/ allows you to get out everything relevant at once rather than just a little.