A trial is lawyers talking to a jury about evidence.
When most people think "court," they think "trial." One judge, 6-12 jurors, and witnesses and evidence presented over days or weeks.
An appellate court exists to review a trial. You have three judges, no jurors, and no new witnesses or evidence.
The judges are the only ones who decide the key question, which is "did the trial judge make any mistakes that ought to lead to a new trial?" They do that by looking at the record. You need to know what that means -- it's the transcript of the trial and any hearings, along with anything filed in the court. It's paper.
An appeal is attorneys talking to each other about a stack of paper.
Being good at trial doesn't help you win on an appeal.
It's as simple as that. This is C-SPAN, not Twitter.
You don't have to take my word for it.
Here's what other reputable lawyers have to say about the role of an appellate attorney:
Writing for the Florida Bar Association, Roberta Mandel explains why trial counsel should retain experienced appellate counsel.
Brian Keller, supervisory attorney for the Department of the Navy, can tell you how an appellate attorney is like a mathematician and why it's important.
I haven't met California board certified appellate specialist John Derrick but I think he's got it figured out. His philosophy, the structure of his practice, fees and progressive consulting, everything. I am only linking to his description of the skills necessary for a lawyer to successfully handle appeals, but I found his entire site soothing.
In another article in the Florida Bar Journal, Jennifer Carrol explains appellate specialization and the art of appellate advocacy.