Hearing is logarithmic, the response is non-linear, ergo you may hear X000Hz but not hear X001Hz, yet hear X002Hz. X003Hz may be easier to hear, yet X004Hz may be more difficult than some. It's not a smooth response.

Take a look at some hearing response graphs to get an idea of how variable it can be across the frequency spectrum.

You may notice that I didn't say it was a universal, inescapable experience for those with tinnitus. The question was why there is any relationship at all between hearing loss and tinnitus, which does hold in a large number of cases.