A lack of resources on the bench meant Mauricio Pochettino was powerless to change things when the Hornets snatched the lead at Vicarage Road.
Campbell told the Daily Star: “If you have got the same players from last season – they may be top players – but you have had a season and a half of the same players to get used to what is coming.
“The problem is that when teams don't spend money, teams set up against you the same as they did last season and they don't have to work you out again.
"They know what they are going up against. Just one or two new players can have you rethinking all your plans.
“They bring a different type of football to the game and different attributes and the other team have to think, 'We've got to watch out for this or that'.
“No doubt Spurs have a few players coming up from the under 19s and under 23s who can break through.
“But you probably need three or four players who can come in for suspensions, injuries or lack of form. They need to be able to step in and not be scared to try to be No. 1.
“If you have three or four players fighting for a position, it keeps everyone on their toes. That is just a natural thing of life."