Okay, so I may have left out a key detail that these "companies" were large ISP's and had massive networks of their own with hundreds of thousands of devices, let alone customer devices on that same network that needed to be managed.

When every set top box, cable modem, customer wifi gateway, and all of your routers/management interfaces need RFC1918 space it goes real quick, real fast.

It gets even worse when you are have to have a lab where you can setup infrastructure that looks/feels exactly like production and thus needs similar setups, now do that for testing/staging... and there's doubling of your required IP space already.