In many communities people dont care about the price of Kosher food, they will pay whatever the price is. I am not talking to those people.
And it some cases the Extra hashghca is just Lmamon and nothing else, there is no reason other than greed to have 2 or more hashghchas at a restaurant
However there are people more on the frindge who make decsions based on price. You can decide which is better to have a higher cost of food vs more people keeping a Mitzvah.
Dont kid yourself the high cost of being frum is a major problem and if not solved will not have a good ending. I am already seeing some negative feedback about yeshiva tutions that people are asked to pay that they cant possibly afford (you cant pay $60,000 in tutions on a $50,000 salaray)