You lose because 1) You arent playing the deck the way they are
2) Different meta exists at 50k DP and that deck could fit well there with the matchups
You need a consistent winning deck to get high DP, but thats just the beginning. Once you pass the 10k barrier decks stop being random and youll fight the decks that beat the random decks. Then you duel the decks that beat them and so on
All in all, players that rank Top 500 of the world may be playing similar decks to you, but they too only have about 60% Win Rate. Played hundreds of games with up to and beyond 100 losses. They adapted their deck to the meta around them and climbed high enough so the only thing that matters in that meta is specific negation/removal and otk strategy. It doesnt work the same in any meta