Re: I'm a network guy, have been for ages.
"If I have a very large scale setup where throwing a cheap box in the bin when it fails is more cost effective than downtime or a support contract with a vendor then I can see an advantage but not much elsewhere."
In large environments (Amazon, Google), you'd go so far as to write your own OS for your switches. Google has been doing this for at least a decade now.
But why does anyone find this strange? We've been doing this on PCes for 30 years. Intel makes a reference design, some integrator assembles the hardware, and then you install Windows 10 on it.
In the case of whitebox switches, the core is mostly Broadcom. Broadcom is the Intel of the network world. Broadcom creates reference designs. Integrators assemble whitebox switches from Broadcom reference designs. Network OS vendors test their OS on various whitebox switches. Yes, the support experience may be fragmented. But the Network OS may be sold via a reseller, who also sells the hardware and can provide support on both together as a unit.
And why would you do this? Well, a Juniper ACX5048 switch/router is about $35,000. The Juniper ACX5048 is Broadcom based. You can get the same hardware from a whitebox vendor for about $6000. You can get a network OS from various vendors, but IP Infusion is probably the comparable to JunOS and it is about $6000. So $12,000 versus $35,000. If you only need data center features, you can get a cheaper NOS.