I'm not suggesting they should have broken up all the teams and made new ones. There are much smarter ways to merge teams that involve gradually easing them together. However, having five teams in the company doing nearly identical things is not "gradually achieving" anything.
If (big if) teams had development plans they had to follow, then those plans should have been adjusted so that eventually all these teams were working towards a common purpose. If you just leave those teams alone and hope for the best not only are they going to avoid any chances to work together, but they will often go out of their way to ensure they don't happen.
How would forcing the teams to merge quickly rather than gradually achieve anything other than messing up everyone's development schedules?