True, those will wreak havoc on a sand filter. I find that the use of suntan lotion, or any lotion or oil, and products such as hair conditioner, fabric softener, makeup, etc... can have a similar effect. It is a much bigger concern for public pools due to bather load, but can become an issue even in a residential pool over time. Sand grains coated in oily substances do not wash off very well and clump together just as those covered in clarifiers do. Even a "deep clean" will not remove it.The only time you generally need to change it is when you use floc or clarifiers that gum up the sand.
The profit margin on a few bags of sand is so minimal as to be non-existent, and the charge for the service, if you choose not to do it yourself, is no more than for any other service provided. Nobody works for free, not even you. You can villainize the pool guy if you like, but be fair and villainize the HVAC, plumber, electrician, carpenter, roofer, and auto-mechanic as well. We provide a service, you do not have to utilize that service if you do not want to. But making out like we are just trying to cheat you out of your hard-earned money is ridiculous. The labor (the expensive part) for deep cleaning a filter is roughly the same as for a sand change, so why not change it and start fresh if you are paying for it anyway?Pool stores and maintenance companies want you to think it goes bad, but it doesn't. They want to sell you the sand and maybe the service of changing it.