I was loosing badly and opponent withdrew, why?

I was white. After I Qxg7, they offered me a draw and I declined. And I could see a few checks but I had no clear mate plan. The king always slipped away in my mind. Why would they withdraw? Did I have a way to mate? Help please


[Site "Chess.com iPhone"]
[Date "01/11/2021 08:54AM"]
[FEN rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1]
[White "maxZamp"]
[Black "puolscores"]
[Result "White Wins"]
[WhiteElo "515"]
[BlackElo "318"]
[Termination "White Wins"]

1.e4 {15:01} e6 {15:09} 2.Nc3 {15:01} d6 {15:15} 3.d4 {14:18} Be7 {15:00} 4.Bb5+ {14:16} Bd7 {14:58} 5.Bc4 {14:10} Nf6 {14:57} 6.Be3 {13:09} Nxe4 {14:53} 7.Nxe4 {13:16} Na6 {14:30} 8.Qf3 {13:20} Nb4 {14:30} 9.c3 {13:05} Nc2+ {14:25} 10.Kf1 {12:43} Nxa1 {14:29} 11.Qd1 {11:51} d5 {14:21} 12.Bd3 {10:58} dxe4 {14:25} 13.Bxe4 {11:07} Bb5+ {14:06} 14.Bd3 {11:05} a6 {13:45} 15.Ne2 {10:49} h6 {12:59} 16.a4 {10:09} Bc6 {12:36} 17.Qxa1 {9:45} b6 {11:44} 18.b3 {8:56} b5 {11:44} 19.c4 {7:33} h5 {11:04} 20.d5 {7:06} exd5 {10:37} 21.Qxg7 {6:13} Rf8 {10:22} 22.Bh6 {3:22} {White Wins}

Thanks, yeah their bishop could trap my queen easily too right?
not sure why they resigned...