I know what you are talking about, and can add another reason. Lawyers!
Short story, we had a customer, a McDonalds that had ductwork from three hoods running to one fan, a fan that was according to the manufacturer not intended for that purpose, (I talked to them myself). Semi adequate access, meaning if it had been cleaned regularly from the start it probably could have been cleaned from the existing access panels. When we got to it, it was so bad that we could not do an adequate cleaning without installing more panels, which they refused to do. We went on cleaning it, writing up reports stating the problems, and for a year the owner would complain because we would not give is system a clean bill of health so to speak.
Finally after a year he tells us he has found a company who can clean the entire system, and doesn't need us anymore. Fine with me.
A year later we get a letter from a lawyer informing us that this store had a fire, we may be held liable and to contact our insurance company. After some investigation of our own, we find out that the store had not been cleaned since we had last cleaned it 15 months ago, and that everybody who had anything to do with that store had gotten the same letter.
Well luckily we had documented everything and had signatures. We made a copy of everything, sent it to the lawyer and never heard from them again. After we contacted our insurance guy he informed us that he was getting out of the Grease biz and we had 3 months to get another carrier. I don't think this incident was the reason for loosing the insurance, I understand that would have happened anyway. Our carrier had already decided to get out of that part of the biz. Our only claim in 5 yrs was for a computer monitor that got wet from a leaky duct.
Now anytime someone tells us they are not using us anymore. We send out a friendly letter, explaining that as per our conversation on such and such date, we no longer are servicing that location, we give them the last cleaning date, and any deficiencies that their system may have, send it certified mail so we have documentation. Just attempting to cover our butt's
Oh and now if we run into a place with access issues we simlpy say this is what it needs and we won't clean it if you don't have this done. Some people understand and get it done, some call you names and show you the door, either way I'm off the hook.