I can't say for sure (never played it or followed it much, because it's not my type of game) but the impression I had is that it was a cookie-cutter attempt to be just another live service online shooter in the vein of Valorant, Overwatch, Apex Legends, etc etc. And people saw no need to play this new one when those games already exist.

Compare that to Helldivers 2 (online-only live service game, same platforms and publisher) which had a lot of personality (the heavy Starship Troopers movie vibe) and some unique gameplay elements like the strategems.

To add, Concord had been in development for eight years at that point, had multiple leadership and direction changes, and then the studio was aquired by Sony because they wanted more big live service games and this game ticked all the boxes and was nearly done. So more money was pumped into it.

And sometimes it works; Apex Legends came out of nowhere and became one of the big live service titles. Fortnite did a battle royale mode out of nowhere and became huge.