(I am not anti-union per-se at all, you can silence me by downvoting but you'll also be creating your own echo chamber in the process)
Nobody's forcing Amazon to not be siloed, but now they are losing a competitive advantage, because this disrupts communication within the company. There's a reason for why its leadership made a conscious choice to not be a siloed firm - and its because silos are less efficient.
It's much like a repressive society that shuts down the internet, because people are using it to organize against the regime. Sure, it's free to do so, but this has negative consequences for its ability to conduct bureaucratic and economic activity.
The difference between a government and Amazon is that Amazon does not have any control over non-work communication channels their employees use - so this move isn't even going to help much.
I don't think they're doing anything out of ideological reasons. Their bonuses and compensation is always tied to their competitive performance. I am sure the higher-ups weighed the potential loss of competitive advantage when making the decision, and given their successful track record, I am inclined to believe it's not going to be as bad as the article is portraying it.
I'm sure they haven't - and are just reacting in the way that any C-suite American executive reacts to a union forming in their company - by making every attempt, sensible or senseless, to suppress it.
This is the first time I am seeing that many people claiming they're upset because Amazon made a decision they think is bad for its own business.