[lokar]

Consider the two steady states:

You are keeping up and the queue is mostly empty, the order does not matter

You are not keeping up, the queue is growing. If nothing changes, the age of items removed from the front will grow and grow, and eventually all be timeouts or abandoned.

[tome]

Oh, I think I see. With a queue the failure state is that everything times out. With a stack you risk sacrificing only the oldest requests and keep the newest alive.

[lokar]

And you end up not servicing some random sample that get buried in the stack before you can get to them.