American Airlines fined $4.1 million for dozens of long tarmac delays that trapped passengers

It depends on how often and how much they get fined IMHO! Yes, 4.1mil is a drop in the bucket, but if it grows larger and on a regular schedule, they will have to take notice.

They stranded us on the tarmac for six hours last year...no apologies and too late to transfer to another airline.

These haven't been ATC issues...these were waiting for signoffs from maintenance, waiting for a part, short a crewmember (so why did they load the planes in the first place)

Lt Col Charlie Brown if they are delayed or cancelled, the airline has to pay the passenger if they can not board. So, get them boarded, and wait. No need to pay them. It's part of the ticket rules and regs. Look into the FAA rules and regs on it too.
If the flight is delayed, i believe , the airline has to pay the passenger a % for each hour delayed from boarding.
If the flight is cancelled, the airline must give the passengers a multiple of a % of the ticket if the airline can't get the passenger a different seat on a different plane. Also, the % is a multiple of the ticket price one way..

Amn Dale Preisach lodging and food is also an additional refund if cancelled / until the airline can get that passenger in the air on a different flight.
I'd also look into getting an upgrade if possible. Unknown if you could get one.

Lt Col Charlie Brown if the airline has them boarded, and a long wait time happens, the airline could say that if you get off the plane, it is uncertain if you could get back on that flight or a latter one since it was " your decision to get off the plane" even though they know the tarmac wait time is unknown and they can keep you there, but not stop you from disembarking.
A good lawyer could get the " your decision " part nullified and have the airline pay for what they knew would be a long wait time and didn't want to pay the fee back to you for each hour delayed.