Truthfully because stans are delusional, and can be psychotic in many ways, and one being if their fave approves of someone elses fave, then they show respect. Seeing as though Gaga, Bey, and Taylor seem to be friendly, and have a mutual respect for one another, their fans follow suit, example, Taylor and Katy fans are complete enemies now, because Taylor wrote Bad Blood supposedly about her. We should just like, appreciate the music we like, and the rest, their is no need to pay attention to it. If you like Gaga because you like Gaga/her work, well that's great
but this is just an analysis of what I see.