We're talking 50 megabytes of storage here, per version. They can save themselves a lot of hosting money by letting lifetime subscribers download the latest version, but that'll cut into their profit margins of course. Even if they don't want to host the setup on their website, providing a 50MiB installer file on request has to be the bare minimum customer support I'd expect.
My experience is that some people do confuse FileZilla with Mozilla. That said, everyone I know just uses the free version, despite the spyware that's bundled with the installer.
Based on this post, I wouldn't buy their professional subscription.