The companies understand one thing: profit.
It depends on the volume of business and a variety of factors. For example, I was recently considering the purchase of a new automobile. There was one make which I ended up removing from consideration because their infotainment was not open for me to hack on. I felt like this was important and so I told the salesman why it was important to me and that this single factor resulted in my no longer considering any models from this manufacturer.
In another instance, a specific dealership had two different sales people contact me by phone, essentially competing with each other. I didn't like that so I didn't bother calling back either one. Several days later I received a form inquiry from the general manager (certainly an automated message). I took the time to respond, explaining that I wouldn't be doing business with them because of the poor coordination of their salesmen's activities. If I already talked with one and explained what I needed in a vehicle, why was another going to call me and try to make me go through all that again?
Granted, these are different examples, but I make this small effort in the hopes that it will either improve the situation for the person who comes along after me or for myself the next time. Of course, the larger the organization, the less likely this is to have an effect. I expect that the GM of the dealership with two salesmen could possibly do something based on my feedback. I fully expect nothing to change from the manufacturer of the car with the closed infotainment system. However, if 10,000 customers all told different dealers the same thing or bothered to write to the manufacturer directly, then something might change.
Southwest and other airlines are by necessity very large companies. If you tell a booking agent something it is almost certain no manager will hear of it. But, if you contact the execs directly, perhaps if there is a VP of customer service or an ombudsman, contact that person and let them know that you value openness and that you are specifically avoiding giving them your business because of their lack of it. If they hear this from enough people, the will get the message: we are losing out on business because of our approach to blah blah blah.
So, bottom line: companies should be as transparent as their customers demand. If you, the customer, don't demand then they won't know and won't make any change.