3. Big teams are pre-occupied with top-flight competitions
Bigger clubs are pre-occupied with other competitions such as the UEFA Champions League and may not necessarily have the squad depth to meet the rigours of another competition. The managers wouldn't want to injure their important players and risk the chance of them missing out on Europe's big nights.
Tottenham Hotspur manager Mauricio Pochettino summed it up like this: “…Tottenham must build a project with the possibility to fight for Champions League or Premier League. Sorry, first of all, the Premier League and then the Champions League. If we are going to try to win Carabao Cup (EFL Cup) or FA Cup, and forget the Premier League or Champions (League), it's a big mistake. I think, what it means for a big team to win trophies, is to win the Premier League or Champions League.”