Quibble or more about your useful exposition, especially WRT:
That's 3-5x growth for the 5 year period. Why has growth slowed? Is it a technological constraint or a lack of investment?
Could be technological. A few years ago I read that magnetic hard disk areal densities were doubling roughly once a year. However, unlike the process node shrinks that allow Moore's law, don't disk improvements come from either small incremental things or huge improvements like giant magnetoresistance (GMR) heads? So the companies could have, for the time being at least, run out big technological advances.
In fact, while I'm not following this at all closely (for various reasons I'm planning on keeping a 4 TB cap on my home storage), the biggest new thing I've read about is shingled recording (https://en.wikipedia.org/wiki/Shingled_magnetic_recording), where writes are partially overlapped, and rewrites are expensive. Per that Wikipedia article, this can add 25% to the capacity of a drive ... which in the context of a previous doubling per year isn't much, it's more of a small incremental improvement.
The other side is demand, of course. I'm not sure on general principles that consumer demand for big drives is down that much, for a small SSD for active stuff + a big nearline drive for media makes a lot of sense. Especially if your Internet connection is capped like mine. This is the approach I've taken since 2007 (with heavy use of high quality CD-Rs for the 2000-2006 period).
Another factor might be an accumulation of people losing too much data on their big hard disks.
Finally, I have to wonder if the big cloud storage providers are slowing down big capacity disk purchases. That'll in part depend on how they use them, do they split out disk farms from compute, or use more homogeneous approaches, such as "moderate" sized disks attached to most machines?