Let's assume that your are right, which I think is true. While courts cannot compel companies to do some things, they can certainly compel them to do things that are a normal part of business, like producing paperwork, or in this case, logging activity.

With an NSL, they could approach a company and require them to start collecting logs and also to not communicate about the new requirement, at which point a privacy-focused company's only choice would be to either comply or stop offering the VPN service entirely without saying why.

Without an NSL, the company would be free to communicate about why it was no longer offering the VPN service, or to announce that they were going to be logging from that point on, giving people an option to stop using the service if that's a problem for them.

But not having a hard drive in place currently, that prevents the courts from getting information about any activity before the court order or NSL is issued, as far as I can tell, which I guess is what those companies are counting on.

Not an easy business to be in, in any case.