It's kinda an ethos thing that goes way back, and Microsoft keeps giving us examples of why it can be a bad idea. Essentially, it boils down to the idea that YOU should be in control of what your system is doing.

Most distros can (including Raspberry OS), and many of them will check for updates automatically, but none that I can think of will install updates automatically unless you purposefully choose to enable that function.

Their purpose is to be used as a base to build your own system, not something for someone to use as-is out of the box.