It makes perfect sense that the sliders start at 0dB and go down to -inf. Maybe you don't understand it, but it definitely makes sense. Everyone who uses dB has also tried a % scale with 100% as 0dB, and then later made a conscious choice to figure out how dB work.
Maybe they're all in a conspiracy to make things needlessly complex. But that's not the only possibility.
Windows has 0-100 volume sliders if you like that better.
They are still some kind of faux-logarithmic*
*behavior depends on drivers/hardware.**
**for some hardware 50 in Windows will be neutral and 100 will be something like a +30 dB digital gain, that's probably in part because Windows is mapping the 0-100 range in some way to the USB audio control range, which is at most +-127 dB or something like that.***
***with some audio interfaces (the non-USB-Audio-class kind) the 0-100 actually becomes a linear factor of 0-1, making the windows controls very useless indeed, as 70% of the slider range does approximately nothing.
Projecting in that context means you claimed what other people think/do, because it's what you think/do. It's about describing the conscious choices of others (where my experience disagrees for example) not about decibels specifically.
Maybe they're all in a conspiracy to make things needlessly complex. But that's not the only possibility.