According to an interview with Friends co-creator David Crane, Joey and Monica were originally planned to be the show's central couple. However, the characters changed when Courteney Cox and Matt LeBlanc were cast, leading to the creation of a softer and more realistic dynamic between Monica and Chandler. This is explored in the season 3 episode "The One With The Flashback," which shows a failed attempt at a romantic fling between Monica and Joey.
Joey refrained from making serious moves on any women in the group, instead treating them like sisters. The deviation from the original concept ultimately benefited the show and its iconic characters.