Why are headings still magnetic?

Andrew Sarangan wrote
So what instrument would you suggest we use for true headings?

Airliners have had 'true heading' available from their INS for
many years.

GPS does not give you true heading; it can only give a true course.

But isn't it 'true course' that I really want to fly? That line
that I drew on the chart? No more correcting for wind, variation
or deviation, just plot and fly true course. Someday it will happen.

Bob Moore