You are correct. THe filter makers have very little interest in the welfare of your fish, but much more interest in you buying their product. That's why so many of them are now going to "biowheels". You can then change the filter cartridges, without getting rid all of your bacteria. I still don't plan on discarding my cartridges very often, but the Penguin I have has extra slots for a more gradual change over of cartridges to allow the new one to be colonized before discarding the old one.
I believe the main issue is that a properly running tank requires very little in the way of expenses. You need to do water changes, complete some tests, etc. But, after the initial investment in equipment, you don't need to buy anything new for YEARS. That doesn't help their bottom line. The real money is in making dechlorinators, test kits, and food. Filters, heaters, lights, etc. are a one time purchase every 10-20+ years. (Unless folks decide to upgrade their tanks.) There isn't even a lot of money in selling the fish, if they are properly cared for, since most aquarium species will live for 5-10 years (sometimes longer) if properly cared for), not to mention that if kept in proper conditions, they will also readily breed (different species more easily than others).
***Make sure to only rinse your filter out in OLD TANK WATER, not under the tap. Tap has chlorine which will kill your bacteria.***