Microsoft Azure, as I understand it, has more data centers around the world than Google and AWS do combined (someone may need to correct me on this, but that was given at a presentation). Microsoft has 52 or thereabouts. Thus Zscaler operates with more than double the data centers that even Azure offers worldwide.
It certainly is not impossible for a competitor to scale out to many data centers, MongoDB does it with their database automatically with their new provisioning functionality.
However, Zs has been doing this for 10 years, and in 10 years there has been no one else to do it, and to do so from scratch to catch up with Zs in a competitive fashion is near impossible at this point in time. You have to come at it from a different direction if you want to be competitive.
In the entire world there is one company that is somewhat similar, although they do use appliances as well (although the appliances are free and part of your subscription). That is iBoss. iBoss is in the visionary square, well behind everyone else other than in vision, and even at that they are behind Zscaler.
According to Gartner there are two other not well distributed possible all internet technologies that may or may not get some play, but I am not all clear if either of these really compete against Zscaler anyways.
So I agree 100 data centers in and of itself is not insurmountable, it is the entire product itself that appears to be insurmountable unless someone tries to come at it from a different angle. To date there is no competitor that qualifies. iBoss certainly likes to market itself as a better option than Zscaler (and they have some sales and VC money, but are way behind and growing well, but still slower than Zscaler). The other two technologies, one involves basically something similar to what Nutanix offers with its DaaS product actually, and that is basically streaming the desktop to the computer. Everything runs on the server and therefore the device on the edge never directly links to the internal network. However, it is not the same as DaaS.
But such technologies are nowhere affecting Zscaler’s business, so I have not dug deeper than a cursory examination (since Gartner mentioned them).
Tinker