We know nothing of why they're shipping once a week.
You might not, but someone who read the article would know:
"Shipping rapidly is important to us for so many reasons. For example, the more frequently we ship the less likely it is for large numbers of changes to build up between releases, and shipping a small release is almost always less risky than shipping a big one. Shipping frequently also requires that we make it downright simple to ship by automating it, so anyone can do it. This raises our bus factor, and also democratizes the process of shipping so there aren’t “gatekeepers” who must sign off before any software goes out the door. And by shipping updates so often, there is less anxiety about getting a particular feature ready for a particular release. If your pull request isn’t ready to be merged in time for today’s release, relax. There will be another one soon, so make that code shine!"