MAF Tuning theoretical knowledge question

I wonder why does MAF cars need to be tuned? Is there something I don't know or understand? As example let's take GM TPI MAF car.
MAF (mass airflow sensor) reads current airflow very very accurately and that I know. What I don't know is why when changing anything in engine like heads or cam we need to retune MAF? Engine draws air in certain speed at certain engine speed correlated to throttle body opening. So if MAF housing does not change MAF will accurately measure amount of air mass no matter if there is stock or aftermarket cam so why do we need to retune MAF when it reads true air mass anyway?
Hope my English is not that bad and You understand my question and lack of knowledge on this subject.

what you don't understand is that a maf isn't a perfect instrument. it doesn't just measure accurately no matter what you throw at it. thats why it's calibrated with a table. changes in air turbulence and resonance etc can require altering calibration. cam changes cause variations in reversion that throw the maf off too. even changing the shape of your air filter will affect maf cal

also you have to remember engines are imprecise too
for example lets say fuel pools up a bit at a certain airflow and never burns properly
and lets say there is no compensation factor elsewhere for that
not everything is just add x fuel for y air and win
itll often show up as a small maf adjustment which isn't perfect but better than nothing

Thank you for the explanation :-)

Best regards