You're forgetting the cost of maintaining a separate machine type for every developer. When models are standardized, the support team can keep identical replacement hardware on hand for quick fixes. They can swap in an identical memory stick or GPU if yours has glitches. They can even swap entire machines by moving the hard drive. Having non-standard machines greatly increases this cost for companies with more than, say, 6 developers. And of course standard hardware typically means a volume discount and a significant support agreement with Dell, or HP, or Apple, or whoever else.
Let's also not forget that when developers are choosing their own machines, they're doing so on company time. It's certainly not cost effective to have developers doing comparison shopping on machines. And it's absolutely not cost effective to have developers putting together their own machines from parts (as some would happily do if allowed).
Let's also not forget that when developers are choosing their own machines, they're doing so on company time. It's certainly not cost effective to have developers doing comparison shopping on machines. And it's absolutely not cost effective to have developers putting together their own machines from parts (as some would happily do if allowed).