Why bit rate is same in a lower frequency spectrum and higher spectrum? If there is a spectrum between 0 Mhz - 1 Mhz, bandwidth would be 1 Mhz here and for example with baseband we can send 2000 bps. What I can't understand is if spectrum is 5-6 Mhz instead of 0 - 1 Mhz, although the spectrum is the same 1 Mhz, shouldn't we be able to send more data because we're sending it with much higher frequencies? Why is bit rate fixated on spectrum instead frequencies itself? What am I missing here?
If you are a bass and sing A 220 Hz and B 247 Hz at 120 beats per minute, you can sing data at a certain rate. 

If you are a soprano and sing two quarter notes A 880 Hz and B 988 Hz at the same BPM, your data rate isn't any higher.

If you sing more notes (higher bandwidth) you could communicate a more complex score (e.g. a higher data rate).  So bandwidth (range of notes) matters, not being a tenor or alto-soprano (spectral frequency).

Same at RF frequencies.