The trap ... which ironically only affects bleeding edge corporations ... is that it's usually cheaper superficially, but doing anything novel in the infrastructure space leads to enormous issues of supportability downstream. For all the complaints programmers have about noobs not knowing anything, or training new hires on company coding standards & practices, it's FAR worse on the infrastructure side.
I'd argue that traditional gear gets in the way a lot more than most people know / would think, but because you can pull any John Q Public off the street to support a Cisco or Juniper environment, "no one was ever fired for buying IBM" applies. Even investments in the common non-core networking gear is usually limited to just a handful of vendors so diversity isn't really a problem in most cases.
I'd argue that traditional gear gets in the way a lot more than most people know / would think, but because you can pull any John Q Public off the street to support a Cisco or Juniper environment, "no one was ever fired for buying IBM" applies. Even investments in the common non-core networking gear is usually limited to just a handful of vendors so diversity isn't really a problem in most cases.