Um, why? Because we don't know what clothes to wear unless we're given a season? What purpose do seasons have other than a very rough approximation of weather trends anyhow? If you're living in a particular climate then the month is surely enough to establish the approximate weather - or you know there's something called a window and you can look out of it and see what the weather is like on the other side.
What purpose do seasons have if they're a very rough and completely inaccurate approximation of weather trends?
Take Canada - or at least Toronto - jokes aside about "winter season" and "construction season", or "cold weather" and "patio weather", the reality is there isn't much of a "spring" to talk about, it rarely lasts more than 2-3 weeks (and it's not uncommon having to switch from heating to AC within the same week, sometimes more than once). What purpose does the European model of four 3-month seasons have in other climates?
You ask why. I think a better question is "why not"?
Interesting idea, but why use arbitary names like 'sprummer' or 'sprinter'? Why not give it a name denoting what it is (like 'rainy season' or 'hotting-up season'?
Wet and dry seasons are already part of the Aussie vernacular in most of the country. There's region specific lingo as well, except in Melbourne where there's just no point in trying to discern what season it is.
It gives me a chance to use a favourite new word I discovered recently...petrichor, which is the scent of rain on dry earth.
http://en.wikipedia.org/wiki/Petrichor
Why do you need to replace one bad abstraction with another? What's the value of having a concept of seasons if they're not something we can agree on universally?
I really don't get it.