However I think I've also explained why I find the information incredibly useful, for different reasons than you. It's an incredibly valuable service to me and most of my immediate peers.
When I neglect to check the weather in the morning, I do things like wear a long sleeved shirt that becomes overly hot in the middle of the day, because the weather had felt slightly chilly that morning. I work in an indoor office, but I go out to get lunch, and it's nice to not be overly hot or cold.
I will say that I find weather forecasts more useful in Spring and Fall than Summer or Winter. Right now, the answer to "what should I wear?" is almost always "thick clothes and a coat!" But then, there are also exceptions, and using the weather forecast to spot them is great.
(Actually, speaking of temperature, something I didn't mention—my apartment is always hot, so even with the window open, it's often hard to judge the current outdoor temperature without an app.)
Edit: Also, whatever your complexion: if the UV Index is 0, you don't need sunscreen. And if the UV Index is 12+, you absolutely should have sunscreen even if you're inside most of the day. It's worth checking!
You have, and your reasons are likewise reasonable - I just struggle to believe that there are so many people that are similar (but again, there clearly are - my struggle to understand doesn't change the facts). People who bike to work, for example, have lots of reasons to care about the weather...yet I seriously doubt that covers a significant portion of people that create the demand for weather apps.
Women tend to have more varied fashion and layers than men, so they would logically be more impacted by weather, yet there's no shortage of men that want that weather info. I get that they do...but I still have troubles accepting that my normal isn't, you know, _normal_.
It's the issue of competing norms - the weather (or at least, foreknowledge of it) doesn't affect how I dress or my activities for 350+ days of the year, over decades, living in multiple parts of the US, so it's hard to grasp that it does actually impact a notable portion of people. Clearly it does, and I've not questioned that (or at least I didn't intend to question that), but having more people tell me that it really, truly does hasn't changed my emotional incredulity that that is the case.