Probably they will have their reasons for several restrictions.
Although Keyboards and PCs both are using bytes, for working as they should they can handle them in a different way, I guess.
Usualy a normal midi song is about 30 kb
For example I have a medley song on my pc which is 273kb and 19 minutes long.
Try to reduce some orders,effects,voices or something like that to work around this restriction my friend.