Question

Why do you think courts of appeals generally limit their review of cases to questions of the law rather than to matters of fact

Answer 1

Courts of appeals generally deal with reviews of the law, rather than reviews of fact. This is because their work is different from the work of lower courts. Lower courts are responsible for looking at the facts and doing investigative work. Courts of appeals only focus on studying whether the trials at these lower courts were done according to the law.

If courts of appeals also did investigative work, trials would become neverending and the timeframe would be unworkable. Moreover, if courts of appeals focused on fact, they would not be able to move on to the next stage and focus on questions of law. This would leave a large gap on a subject of great importance.

Answer 2

Because the facts were dealt with at the trial. 
You were convicted there. 
The appeals process is to see if matters of law were violated in your case. 
That is why you must have "grounds for appeal" for your appeal to move forward.