Why not ? Because a Software Defined Network (SDN) is not a thing. It is not a single thing, SDN is a built thing made of many elements.
You can’t buy a “routing protocol”. You don’t buy a “security strategy” or a “network management“. You don’t buy a “data centre”. All of these things are built or developed by a team of IT people and various vendor products or open source tools.
You can buy :
- custom hardware or commodity/open hardware
- vendor software platforms or people who can deploy open-source or vendor software
- people who evaluate and make decisions on best choices for your situation
- people to operate your network
Then you have to put the parts together, smooth out the interfaces and make them work for your business.
Thats why you can’t by an “SDN”. You have to build one that works for you.