So three tips.
First, I would suggest paying very close attention to the actual wording of the prompt, and make sure your essay actually reads as a thoughtful response to their specific prompt. This may sound cynical, but I think the sorts of colleges that get a lot of cut-and-paste “shotgun” apps are, among other things, varying their prompts from others, or possibly even over time, in ways partially designed to help them identify such applications.
Second, the easiest way to write compelling, personalized Why Us essays is to actually have a really good process for selecting colleges for your list.
Like, to be blunt, if your ACTUAL reason for applying to a college is the US News ranked it its top 10 National Universities, or it is in the same athletic conference as Harvard, or it would impress your peers if you got admitted, or your parents are making you apply, including because it would impress THEIR peers if you got admitted, or so on . . . well, those are not good reasons from their perspective. And since your honest reasons would likely end your chances (although I bet they would get a laugh if you did write, “Because my parents made me!”), you are then stuck trying to fake it. And there is a lot of advice online that is basically about how to fake it, but they know about that advice, and so it might be harder to fake it then you hope.
And some kids will likely pull it off anyway (and be happy to tell everyone about it). But lots and lots of highly qualified kids get rejected by colleges they applied to in this fashion (although they are less happy to tell others about that), and while we will never know for sure why, I believe a perceived lack of authenticity and true reflection in their applications could in fact be why in a lot of those cases.
OK, but if you instead pick your colleges because you really think about what you want in a four-year college experience, academically and non-academically, and you identify the colleges that are actually the best fit for you . . . I think you can basically just tell them that. But maybe with a little reflection on what they are actually looking to learn from these essays, which leads me to my last point.
Third, AOs I have seen discuss this sort of essay tend to emphasize they are not so interested in seeing facts about their college. They know that stuff already, and your ability to look it up too is not particularly impressive. They are also not so interested in hearing about your plans for after college. That is not really their concern, and they also know many, many kids change their plans anyway. And in fact–and this is tricky–they are not necessarily all that interested in exactly what you think you will do at their college, because even those plans often change.
So what does that even leave? Well, what they are really interested in is you. What do you value? How do you think about important decisions? What process do you follow? Are you open to changing your mind? All sorts of stuff that they might not actually be able to learn from the rest of your application.
So this is pretty vague, but I would spend some time reflecting on what your process for choosing colleges on your list shows about you. And then if you are happy with that answer, you can make a point of showing (not so much telling) that in your Why Us essays.
And if you are not happy with your answer–again, I would resist the temptation to fake it. I would instead take a step back and follow a process for choosing colleges you can in fact be proud to explain.