Because, for example, the native U.S. rocket and booster business--and aerospace industry in general--is slowly disintegrating.
The Russians are dumping hardware because they are desperate for hard currency. Much of the hardware was developed when they called themselves "Socialist", and basically had no price since there was no way to compute economically-valid prices.
"Thank you for helping win the Cold War," U.S. aerospace workers are told. "Now go stand in the unemployment line while we buy cheap hardware from the enemy you helped defeat."
Let's see: Shuttle grounded. No more Titans. Atlas-V dependent upon a potentially hostile foreign source of engines. Delta-IV limited to military payloads only. Delta II nearing obsolescence. But let's go ahead and let what is left of the U.S. aerospace industry (particularly the launcher part) vanish into rust, and put our trust in people who tried assiduously to kill and/or enslave us all for 70 years. That's the ticket.
--Boris