It's a bit like asking why anybody would want 100x the amount of any computing resource they have right now: jumping up more than an order of magnitude typicall

It's a bit like asking why anybody would want 100x the amount of any computing resource they have right now: jumping up more than an order of magnitude typically enables completely new use cases. For every step up those use cases have to be discovered, and it might just be that we haven't discovered too many compelling common use cases for gigabit networking. Maybe they don't exist, but I would think it's more likely they just haven't been discovered. At this point it seems a lot of use cases like remote work, collaborative editing, games are more obviously limited by the (often physically unavoidable) latency. Another limiting factor is that it doesn't help much to have gigabit networking if either side limits the actual bandwidth used.