Porting games to the web is a fun hobby! I've done Quake III [1] and Cave Story [2]. Just like in this story it's all about the details. Getting the game loading is just the start. Things like adding touch controls for mobile, handling multiplayer, managing save files, supporting modern screen resolutions and frame rates, they take more time than the initial port.
[1] Single player: https://thelongestyard.link/q3a-demo/ Multiplayer: https://thelongestyard.link/q3a-demo/?server=HN