You hate to see stuff like that. I keep my vehicles very clean on the inside. Only thing that happens is I get a little mud on the mud mats in winter and they need to be hosed off in spring, and of course bits of dirt, gravel and grass track in off your shoes and collect around the edges of the carpet, and I vacuum it out periodically to keep that to a minimum.
My Chevy had two stains in it, but they were both -my fault-. You see, the original owner of the truck was my father. "Kid me" had a soda fly out of my hands when Dad had to hit the brakes suddenly twenty or so years ago and it stained the passenger side door panel, and a bite size snickers bar somehow got under the seat and melted into the carpet in the summer heat back in 1994 or so. (That one may have been my sister's fault, but I'll take the blame for it too.) My door panels started to fall apart, so I replaced them both last summer with aftermarket replacements made of newer/better materials, so that finally got rid of that stain I'd tried so many times to clean over the years, and that chocolate under the seat I mostly scrubbed out with resolve carpet cleaner long ago when the truck still belonged to dad.
My bench seat, miraculously, still looks almost brand new. I cleaned it recently for good measure, and purchased a seat cover that matches the interior to continue to protect it and keep it nice. I cannot understand people that let their vehicles get nasty like some of the descriptions/picture/stories you all shared. You hate to get in and ride with someone whose vehicle is that nasty. I know people who have vehicles that are only a couple years old, and they are straight filthy inside. My Chevy is 25 years old, and it has a discolored spot where a snickers bar was in the carpet under the seat un noticed for a few years, and that's it. People seem to be somehow shocked to ride in my "old" truck and see it look detailed and clean inside. It isn't hard, I think many people are just hard headed.