The reason that integration mergers are so popular is the same reason why they commonly fail: They are designed to simplify management by forcing the acquired company into the mold of the acquiring company. If we were talking about a marriage, this would be like surgically connecting the bodies in order to limit the differences. While small mergers, like transplants, can be made to work, large ones tend to be too shocking to the entire entity, and the operations fails.
And:
Dell and EMC's big mergers, on the other hand, follow a different path. Management's desire to avoid special training is subordinated to the need to protect the expensive assets that have been acquired. The first steps aren't to rationalize the processes between the firms but to identify the top human and physical assets (including customer relationships) and make sure they are first protected and then enhanced. This process was first developed at IBM after a huge string of expensive acquisitions that Big Blue destroyed, and Dell and EMC (including subsidiary VMware) have improved on the process.
This reminded me of a portion of the (excellent) book Soccernomics where the authors discuss transfer fees for big-name football talent. It turns out that, in the aggregate, the amount of money that clubs spend on transfer fees has almost no bearing on league position (essentially, wins and losses). A team that spends $50 million on transfers is likely to perform (on average) about as well as a team that sells $50 million worth of players and uses those proceeds elsewhere in the club.
Obviously, some transfers must be successful (I don't pretend to really know anything about this, so I'll defer to other sources who suggest that Cesc Fabregas is a strong example of this.) But it must follow that if we can produce 50-person long lists of successful transfers, there must be very lengthy lists of transfer failures.
Interestingly, the authors of Soccernomics point to a very significant contributor to these failures: a nearly complete lack of effort to integrate the players into their new communities. Take a young, talented player from Brazil and stick him somewhere in the French countryside with no support (principally language support) and see just how successful he is.
This is analogous to flippant M&A activity. Much like football clubs spending $20m on a player but less than $10k to get him settled into his new country, irresponsible acquirers will spend a hundred million dollars on a new asset but barely consider integration strategy.