That really depends on the publisher. Most manga companies simply license already released series and they can put them out on a quick schedule. As for Seven Seas, our works are original and it takes time to make them. ^_^
You'll be happy to know that we're putting the finishing touches on Amazing Agent Luna Vol. 2 as I type this. It'll be off and at the printers so very, very soon. ^_^
I had the chance to go through and copy edit the volume today...and, trust me, you're absolutely gonna LOVE it!!
work on it, and compare yourself to supirio people all the way. this will lead you to try to improve. Learn from everywhere. but most of all, even if you have other people do stuff for you, try to do it yourself.