When have corporate owners ever been shy about blaming taxation for any and all business ills?
Public records show that 2 quarters of large losses, a downturn in world wide smartphone sales, stringent and expensive deals with Apple as well as being purchased by Avago Technologies and left with a big debt would be sufficient reasons to back out.  They don't need the plant anymore and don't feel it necessary to hang on to it for future needs.  The company made no mention of taxes at any government level.  Frankly the historic volatility of all chip markets makes Broadcom a bad fit for Eugene or any community looking for a stable employer.