Or because the servers went offline or the company didn't bother to keep the source code. A few years ago, there was a really bad remaster of one of the GTA games where it turned out they used the mobile version of the game as the source code because Rockstar hadn't bothered to keep a copy of the game. There was another time where it turned out that the copy used for a remaster of a game was a cracked version of the game, and people could tell because they hadn't even bothered to remove the cracker's logo. It's estimated that over 50% of games are now gone forever because companies just don't bother to preserve copies of the source code.