Here are the facts:
Morphy has a total of 466 known recorded games (of which 4 are in consultation). 89 of those games are King's Gambits.
Morphy played white in 71 of the 89 games.
Of those 89 games, 72 are KGA and 17 are KGD.
Of the 72 KGAs, Morphy played white in 55. Morphy lost 11 and drew 3.
Of the 17 KGD, Morphy played white in 16. Morphy lost 2 and drew 2.
Remember, many of these games were play in simuls, blindfold or at odds.
Good, meaning he played 71 of his games as white versus 18 as black, out of a total of 466 games, most of his opponents playing 1...e5 at the time. Some 15% of overall games. How about the Evans gambit or the Italian game? To make a comparison.
He played most of his KG games (and Evans Gambits) as white simply because most were from simuls, odds or public exhibitions. I don't intend to do a lot of data crunching here. I'll just mention about the Evans Gambit, David Lawson (Morphy's biographer) wrote:
"Yet of all the Evans Gambits Morphy played (some eighty on record), he lost only two even games, one other to Riviere, and a few when giving odds of Knight or Rook. Whether he offered or was offered the Evans Gambit, he almost invariably won, regardless of odds."
Hm, it is like he played some of its openings that he thought at the time to be inferior almost on purpose.
I'm not sure what the purpose is here, but, for some purposes, it might make sense to just consider Morphy's major matches against Loewenthal, Harrwitz, and Anderssen. Perhaps also consider the Paulsen games in the 1857 tournament. Maybe also the rest of the 1857 tournament games.
see link
http://www.365chess.com/players/Paul_Morphy
You'll also notice that he did play 9 games in the king's gambit accepted, as black however.