Anyone who didn't see those barriers wasn't looking
And you missed two.
Integrating existing in house software solutions, particularly legacy ones, is a significant cost, or a significant loss in functionality.
Even if you have the resources to surmount the above do you have the people and do they have the training.
Cloud proponents real problem, is they keep spouting off how great and brill and cheap and new it would be, completely ignoring the costs of getting there.
The cloud is a different platform, so they make as much sense as a linux fanatic walking in to a windows shop and telling them all their problems would go away if the switched to Ubuntu.
Doesn't matter if said fanboy is right, the cost of doing it is outright hideous. It's a huge up front investment, a massive bag of risks, and for any one just back from visiting their home on the planet Zarg, there's a recession going on at the moment.