Once you get a theme approved, understand the basic requirements and follow the forum for currently trending soft reject reasons, soft reject count will be at the max one from next theme onward or even direct approval.
Proper escaping, global variations not allowed except in function are few of the examples which are discussed from may be last 6-7 months, still every other day a new thread is created to get suggestion as if it is mentioned for the first time.
I agree these requirements should be mentioned at one place officially, but in business we are responsible for our own time. There is a thread for most common soft reject reasons ( of course not on design basis 
), if you check that you will notice maximum reasons you have got already listed there.
Go ahead and mention there if you have got some extra reasons, that will be helpful for others too.