Simple: It needs to bulk up to contend with the might of Apple, one of the largest buyers of flash memory.
Samsung has supplied the memory chips for Apple's iPhone since its launch last year. Before then, Samsung sold Apple memory for its iPod line, and continues to do so today. Apple is a huge customer for Samsung — so huge that it can command deep discounts, and tie up an enormous amount of Samsung's manufacturing capability. When Apple first launched its flash-memory iPod Nano, it locked up enough production to keep rivals off the market for months. (Even Samsung and SanDisk tried to launch me-too clones of the Nano, to no effect.)

Regulators may block Samsung's SanDisk bid. But they ought to keep an eye on Apple, too. Antitrust cops tend to spend all their time watching for monopolies — sellers who wield undue influence over a market. They should crack open their investment glossaries and look up "monopsony" — the condition that exists when a buyer dominates a market.

(Illustration via Apple Insider)

There is nothing wrong with the products so we aren't accepting returns from customers ... [Customers] understood that there were two competing formats and understood that one of them would probably prevail ... so they made the decision to go with HD-DVD... [Toshiba will] assist customers in understanding the benefits of the products.