Ann: Investor Roadshow Presentation, page-85

I'd guess the Seven logic was that free to air TV is in trouble, the mining boom is over thus hitting that part of their business so they need to diversify into something else.
At the time there was big talk about Gas shortages and massive Gas price Rises.
They looked at companies out there and at that point in time BPT/DLS were the best two to benefit from increased gas prices and oil prices.
Unfortunately for them prices kept falling so I think they gambled and got it wrong.
Had they of waited and started buying now we would have a totally different scenario as other predators would likely be buying both BPT and DLS at these levels.
The seven holding in my opinion is holding back takeover bids from other companies.
The best option for Seven is to contact other predators and offer to sell their stakes to them at a premium so that the other predator can take both companies over.

A merger of BPT/DLS will not be as beneficial to Seven as a takeover bid from a third party company.
Seven also does not have the cash to take both companies over.