I daily drive Linux and I kind of agree with you. The amount of people I know that use Linux, use non-dev apps on their laptop/desktop, and aren't developers are zero (excluding myself obviously). The actual percentage of non-dev native gui tool users on Linux is probably within the noise of the measurable data.
There are plenty of people who daily drive linux that would disagree with there being "zero use cases"
If you ever are curious about how product managers make their decisions, it's based on more that 'plenty of people'. If you want to be a good engineer, you should also learn the difference between zero and approximately zero, if you want to quote people.