Yeah. It's a mixed bag of benefits and (in)convenience. The Sierra/Silverado GMT-800's began the cabin filter option in 1999. It was later discontinued about 2004-ish, with the reason given that owners weren't servicing them, and complaining about poor HVAC performance due to that. Initially, they (GM) just left out the filter panels, but the option of installing them was up to owners after delivery. At least one model year omitted the access cover opening, so they couldn't be used even if you wanted to (although they could be easily mod'd to accept them). I think it was more of a bean-counter decision, but facts remain. If filters are plugging up, whatever it is that's plugging them is being passed through the system w/o filters, and onto passengers, or allowed to block airflow through the evap core. Poor HVAC performance will almost always result in a dealer visit, at least on in-warranty vehicles. Maybe GM figured out that despite the health and comfort benefits of cabin air filters (I doubt they give a hoot about that), the additional maintenance item would be overall beneficial to dealer service departments bottom line, and almost all GM vehicles have them, since. Generally, people don't read their owner's manual. There's profit in ignorance, willful or not. Later models are MUCH easier to service. On my 2001, the lower HVAC cover has to be removed (3 blind screws and a thick, semi-rigid cover that doesn't remove w/o distortion), and one screw retains the filter slot cover. Once the cover is removed and filters slid out, any debris caught by them immediately dumps out on the floor (easily avoided, but not mentioned in the manual, BTW). The passenger cars have them easily accessed behind the glove box, which is about a minute to remove. Our 2017 Volt has a carbon/charcoal filter, which provides noticeably fresher air (why aren't all of them like this?). If an owner doesn't like the filters, they can just leave them out. The system will function as before w/o them. A benefit of having the option, whether or not filters are used, the access cover opens immediately before the evap core, and allows for MUCH easier removal of debris that may block airflow, as well as cleaning of junk that leads to mold and stinky air. I like them, and will continue to service them.

In your case, a filter option (however effective) may have prevented this thread, entirely. Low airflow is a simple issue to diagnose, and having a likely suspect almost always makes it a simple process. Not unlike MAF codes, the usual suspect is almost always a fouled air filter, and we almost never hear about them because they aren't worthy of discussion. We'll hear about the occasional duh moment, but they are the exception, not the rule.