i dont see any good reason as to why someone would lie about their age on the internet either but they still do it
that's not even a good brown townogy because there's a valid reason to lying about your age on the internet
a lot of sites have age 13 restrictions and if you're 10 you'll have to lie about your age to get the stuff you want in that site instead of waiting three more years.
as to lying about having tulpas, you wouldn't even gain at all from lying about tulpas than if you were to just stay silent about it.