Flash storage is a victim of its own success
All-flash storage ages better than disk based storage. It consumes less power, generates less heat, and is not subject to mechanical "wearing out" like HDDs.
The concerns about flash wearing out due to writes was overstated based on the nature of I/O and data. I/O is more read than write, and as data ages it is updated less.
As a result, all-flash arrays have a much longer useful life than HDD based arrays. And many enterprise customers have stretched the amortization of HDD based arrays out to 4 and 5 years compared to the typical 3 years in the past. Customers expect to keep arrays for 5 years now.
In some ways this is like electric cars vs. gasoline cars. The electric car requires less maintenance. Other than tires, it has fewer parts to wear out (things like regenerative braking mean less wear and tear on brake pads and rotors). No belts and hoses, no radiator, etc. There was the concern the batter would wear out in 5 years, but the battery wear out issue, like the NAND wear out issue, is not as bad as expected.
We are now at a point where most enterprise customers have replaced their older high-performance HDD based systems (i.e., 10K RPM and 15K RPM SAS and FC HDD arrays) with all flash.
The result is there is less churn in the high performance array space. This means the all-flash array sales curve is flattening as this wave of initial sales is completed, and there will be more time between that initial wave and the replacement wave.