That is a great question!!
Actually my previous workplace is consolidating businesses as we speak. I am certain that the only work going into it is cost reduction/headcount reduction and burying poor financials of one business into a consolidated statement where it cannot be seen. If you never have the same baseline then how can shareholders see the poor performing businesses right?
The real question here could be: if the intent of the merger is to bury skeletons, even if due diligence should happen (likely it does) would it ever happen??