I've been exclusively using Linux for almost a decade now. I started in high school when the computer we had at home was painfully slow with Windows. At start, it did seem a bit hard to wrap my head around. I was a kid, and there was no one who used Linux to teach me. I guess the installation etc. are much simpler nowadays. And the online spaces are much less toxic.

Even after all that, the main reason, I believe, is that it's different. If someone is using a stable distro like Debian, and just wants to do what 90% of people do (i.e. browsing, looking at documents media etc.), Linux isn't really a hassle. The installation process might be daunting to some people. But after that, they don't need to open a terminal ever if they don't want to. My sister is basically tech illiterate, and she's been running Mint for a few years now. Never heard any complaints. Only issue she had was when she deleted her .config folder. But I had set up a script that backed up dotfiles to her external drive, so it was easily fixable.

People get frustrated because whenever something happens on Linux, and they go online, they see all these walls of text that they need to read, and commands they need to run. But they forget that on Windows and Macs, that isn't even an option. Most of the time, you need to reset your system. Or, in the case of Macs, get it replaced. The frustration that people experience is caused by conditioning. They accept the inconveniences of Windows and Macs because they grew up with it. But since Linux is new to them, the shortcomings stick out much more.

TL;DR: For the average user, the OS doesn't matter (they should probably still use Linux for increased privacy). For the power user, unless some specific applications they need are missing, Linux is always the best choice. The frustration is mostly due to conditioning.