Doesn't this show that the executive layer of Amazon isn't as clever as they appear? Employees can organize easily on Whatsapp or any other platform. In that case, Facebook has all the data and Amazon doesn't have any insight. Facebook then can hire any disgruntled but competent employee easily.
The lock down also signals weakness and insecurity. Amazon pays at least market rates and people want to work there. In case of a strike, they can hire new people with no training because workers essentially shop all day, a skill that is ubiquitously available
I don't find that to be an entirely realistic scenario, but we can talk hypotheticals. As a company owner, I would welcome the opportunity for employees to quit as an alternative to unionizing. Having your problem quit for another job before you have to fire them is awesome. Having a competitor actively recruit your problem employees? That's killing two birds with one stone. You have to just laugh when it happens. It's great.
As for discouraging unionizing via official company communication media, it probably has more to do with discovery and access than wanting to block the communication altogether. Of course they realize people can use Whatsapp, text, online forum, etc. The thing is there needs to be a way to discover a large community of workers on some other platform. That's much harder than going through a company directory or blasting out emails to entire divisions. They don't want to provide easy discovery and access to people who would potentially join a union.
The lock down also signals weakness and insecurity. Amazon pays at least market rates and people want to work there. In case of a strike, they can hire new people with no training because workers essentially shop all day, a skill that is ubiquitously available
What do they fear?