Are you familiar with them, because they actually recommend CleanMyMac and indicate it is safe.
"They" are being compensated or otherwise benefit from the products they promote.
You will not find a website that says "do not use this product" because no one profits from doing that. They will say it's "safe" or "recommended" or "highly regarded" or whatever. The reason is simple: 1: you have a Mac, therefore 2: you have money, and 3: they want it.
That is the beginning, the middle, and the end of the world's oldest story. It will never change.
"Cleaning" apps are scams. Excerpted from Effective defenses against malware and other threats:
Never install any product that claims to "clean up", "speed up", "optimize", "boost" or "accelerate" your Mac; to "wash" it, "tune" it, or to make it "shiny". Those claims are absurd.
- Such products are very aggressively marketed. They are all scams.
- They generally operate on the flawed premise that a Mac accumulates "junk" that needs to be routinely "cleaned out" for optimum performance.
- Trial versions of those programs are successful because they provide the instant gratification of greater free disk space.
- That increased space is the result of irreversible destruction of files, programs, or operating system components normally protected from inadvertent alteration or deletion. The eventual result will be unreliable operation, poor performance and random crashes that may not become evident for months or even years after their use, when updates to programs or macOS are eventually released.
- Memory "cleaners" that circumvent macOS's memory management algorithms work by purging inactive memory contents to mass storage, which can only result in degraded performance and accelerated hardware failure.
Generally speaking the more aggressively a product or service is promoted, the more you should avoid it. "Cleaning" apps for both Macs and PCs have made a few people very, very wealthy. They have also left orders of magnitude more Mac owners very, very miserable. The cost in terms of wasted time, productivity, labor, lost data, anger and the general parade of horribles they cause must be incalculable.
