I think expectations have grown astronomically since 2004, budgets have ballooned, graphical fidelity and animation quality has skyrocketed, development team headcounts have gone through the roof and many games just have more systems than they did before.

Games are less frequent because they take a lot longer to make, I read the other day that Halo 2 was apparently churned out in 10 months, these days even games building on other games foundations such as Tears of the Kingdom can take 5 years to come out.