Comment by ryandrake

Unfortunately, we are living in a world where we need to treat every third party application that we run (and in some cases, even the operating system itself) as a hostile attacker.

Gone are the days when you could download a software, run it, and trust that the developer isn't transmitting everything on your system back to their servers. Developers have poisoned the well and repeatedly demonstrated that they will run roughshod over the user's system, send telemetry back about everything the user is doing, enroll them in A/B experiments they didn't ask for, and take advantage of every resource, every peripheral and device, and every bit of personal information they can get their hands on.

Unless you are 100% running open source software that you have personally vetted, or that you trust that the package manager / maintainer has sufficiently vetted, you can't copy a password into the clipboard with any kind of confidence that other apps aren't sneaking a peek.