The only thing that happened post merger was ticket prices went up, parking went up and cable costs skyrocketed ...
Why did this happen post-merger? For the same reason why the NBA and NHL went through the same consolidation process in the 1970s: television. Before television, teams generated most of their revenues through ticket sales and merchandise sales. When that was the case, it was common to see regional sports leagues to exist all over North America. Television put an end to all that because each team now had the ability to broadcast to a national market. It was inevitable that TV contracts would eventually be governed by sports leagues instead of individual teams, because these leagues couldn't maintain a competitive balance on the field if they had to deal with the dominant teams broadcasting into the smaller regional markets.
TV helped, but it wasn’t the predominant reason - there was no competition. If the Miami Dolphins were charging $120 for basic seats plus $20 parking and $15 hot dogs and the Miami “Hurricanes” in an alternative league were charging $40, $5 and $5 for the same thing, which do you think most would go? Same thing at the TV level. When you are the ONLY game in town for that, you can charge big bugs.