MKMatty
¯\_(ツ)_/¯
I don't really like the sleeves either, but it seems like majority of these pre season ones that people have got are long sleeve. I've seen another 4 or 5 that all are, so maybe being pre season (pretty hot in most parts of the country) they were never used or needed so they were the ones framed up and sold/auctioned. Both on mine are long sleeve and both look to never have been worn, brand new, no pilling, no marks or anything, so they were likely signed and framed straight away.
I imagine those cotton jumpers would make be pretty warm to run around in. Factor in warm weather and I can understand why players would rather not wear them.