Yes, because Amazon lives their life just like you do, and makes decisions on the spur of the moment.  <eye roll>

They'd been fighting this tax battle for literally decades.  They saw the writing on the wall.  They made a calculated decision.  They determined that they were eventually going to lose the tax collection battle, anyway.  They decided the "state presence" situation was irrelevant because of that.  

One of the reasons why Amazon fought the sales tax battle so vehemently for so long is because they were working to make themselves a viable option even collecting taxes.  Once they reached the break over point it didn't matter anymore.

When a multibillion dollar corporation announces something like the fact that they're going to start collecting sales taxes you can bet it was a decision that had been made many, many months before you knew about it.