People are affected by different things and find different things difficult.
I can cope on very little money, try to live on e.g. £159 for the last 10 days of the month, go without things I'd like, not be able to do anything - and not bat an eyelid whereas some else might get upset at that.
I cannot cope as easily with the weather being like this after such an awful winter (especially of not feeling well).
It's all well and good to say about people being outdoorsy and yes, I was in the past, but if you cannot walk much and need to sit, it really is not pleasant trying to sit out somewhere when it's e.g. 12C and drizzling.
Compare that to early mornings of bright blue sky, a sun-filled day, and the possibilities open up massively. Spending the day outside. Eating outside. Sitting under a tree. Being able to go to a park, sit and watch the animals and birds. So yep, it does make a difference and I don't think it's a little thing. Of course if what you love is indoor activities then yes maybe it doesn't make as much of a difference but people have vastly different preferences and things they find fun and nice.
In the past, when I was 100% healthy and fit then yes, it was more manageable but that doesn't mean I wouldn't understand that for some people it wasn't.
So no, OP, you're not being unreasonable.
I wonder if we have become spoilt with such good springs and early summers over the past few years.
I hope it picks up for both of us soon :)