I have some non Bambu filament, but I really like just being able to toss a spool on the AMS and have it know what color and it is. Sure it only takes a few seconds to manually change it, but I personally like the convenience and can afford the slightly higher premium. I have had some minor issues with some of the off brand filaments where I have never had any with the Bambu stuff.
Whether you think it’s a dumb marketing strategy or not, all that matters is what the customers actually buy, and what the Bambu bean counters see. Not much different than any other printer. You can always buy 3rd party ink/toners, but the OEM ones still sell just fine. The business model of selling those printers cheap (little profit) and relying on sales of supplies (large profit) has worked for many years.