Yes, I can understand how that might frustrate you. The airports typically are responsible for the internal transportation assistance such as carts and wheelchairs although some airlines keep wheelchairs on hand also (because they have determined that they cannot always rely on airport transportation).
Were you able to ask for assistance at the original gate and then unable to get any help? The conundrum in asking is that while waiting to ask, time is lost, and while waiting for transport, and time is lost.
Last minute gate changes are typically due to weather or aircraft changes. I have also seen changes overnight where one gate is posted when I go to bed and by the time I get up (even if just a few hours), the gate has changed....and it is always changed to the last gate of the terminal, which means it was probably a cost saving measure—-less fuel used to park at end rather than pull past all the other gates, but that change comes with a warning of a few hours.
Sorry this happened to you, and I recommend that you let the gate agent know about any hearing difficulties when you arrive at the gate so they can be aware and on the look out for someone who needs help. (Gate agents often arrive at the last minute, so it may be helpful to perhaps carry a printed note that you could leave on the desk for them as you arrive. No guarantees this would work, but it increases the odds).
I hope future flights go smoother for you.
