This was when Bruce Banner still had a story with supporting characters, so tying in Betty Ross, General Thunderbolt Ross and even enemies Annihilation and The Leader actually worked. Part of what happened with Norton not playing Hulk anymore was that the MCU sort of shifted the character to a supporting role. Edward Norton wrote dialogue for Incredible Hulk, and in 2018 famously took Marvel to task for not making the Incredible Hulk film better – hoping that it would be as good as a Christopher Nolan film.
There’s been a lot of back and forth as to why Edward Norton stopped playing Hulk, but the truth is somewhere in the middle. It was partially because of money, partially because of the new character arc for Hulk, and partially because Edward Norton is difficult. Mark Ruffalo is a different Hulk and had Edward Norton remained in the role it’s possible we would see a different Hulk. All in all, it worked out for the best.