Comments on https://lichess.org/@/shaveensilva28/blog/how-good-is-the-kings-gambit/gjTiXL4z
I'd say it's fine for about up to 1800 FIDE being an ex-KG player. It still can be a good surprise weapon in blitz at higher levels. The problem with the KG is that it's easier for Black to get a draw (g5 lines), and the modern variation played with the Falkbeer move order which I believe can also be used with the bishop's Gambit, Black is slightly better even. Too easy for Black to memorise what to do, then it's an uphill struggle, but some like that. White can also be going for a draw and lines like the classical declined can be difficult for Black to keep the position interesting enough to play for a win.
The other reasons for it to fall from grace are there are lots of lines for White to have to know how to play where dividends are probably better spent on more reputable lines, that romantic tactics often fail to surprise in long play as Black will work out how to give material back (though in blitz could get overwhelmed). I guess fashion also plays a part.
Id say it's a very good opening for blitz players and it may confuse players and take time when playing this opening