As I already pointed out, it's often a case that the WIRING won't support Gigabit
Have you tried what 5e can do?
You are ASSUMING 5e - a lot of businesses have 3 for wiring, not even 5 much less 5e or 6.
And yes, I know the limits of using 5e with Gigabit (works but keep the runs fairly SHORT, or go 6 - and for serious backbone work go 6 period).