It's extra-frustrating writing those instructions, because not only are they platform-specific, but they are different depending on what the user has already done to their system. If some other tool told them to create ~/.bash_profile or ~/.bash_login, the more shell-agnostic option of modifying ~/.profile will no longer work.
Figuring out where to change the PATH is also confusing, and you might come across solutions that seem to work, but cause weird errors later down the road. For example, the tool being unavailable when invoked remotely, because you only changed the PATH for interactive shells.
It's understandable that people use sudo when they don't see it causing any obvious problems. Installing user-local packages should be one simple command, and it's a failure of operating systems and package managers that it's not. As it stands, correct usage is much harder than incorrect usage, and this is the result.
