Itch.io does not have a music player, so the voters must download the tracks in order to listen to it, which was unintuitive and a hassle to do as they are not only listening to one entry. Based on past jams, submissions which only submits on itch.io and does not upload their tracks on streaming sites gets less ratings than ones that do, so we decided to make it a requirement to make it fair for everyone, and it makes rating a lot easier as well.
As for the file type, we chose .mp3 as it's the most common and every computer should be able to play it, and it's also pretty small. It's also to keep it consistent across all entries. There are also lossless options (.wav and .flac). Hope this makes sense!