There's big money in e-discovery. At least for the lawyers and vendor making e-discovery tools. The enterprise being targeted is the loser because of time, effort and cost to dig through all of that stuff.
I suspect that many companies are keeping too much data because they don't have a strategy well enough defined to outline a use or purpose for that data. Then, since storage is relatively cheap, they keep everything.
The flip side of that coin are the companies run by executives who've been bitten before by lawsuits and keep everything for CYA purposes.
Either way, it's to the company's detriment to keep absolutely everything. Decide what you need and keep that. Much better and more effective than keeping everything and eventually (or not) deciding what you need.