It appears that the sheer size of the merger was largely responsible for its refusal. A merger would have created a huge amount of product overlap, led to numerous management departures, not to mention the many potential antitrust problems. Seagate has a market value of about $6.9 billion, and while Western Digital has smaller sales, its market value is at a larger $8 billion or so. Unsurprisingly, neither company was willing to comment on the news.
Last week, Seagate ended acquisition talks and started buying back $2 billion of its own shares. Talks collapsed after TPG Capital couldn't find other partners to raise the required amount for the takeover. For now, it looks like Seagate is content with continuing on alone.