Why the third movie in a trilogy almost always sucks

According to Rotten Tomatoes’ rating of the 70 highest domestically grossing trilogies in the US, 64% of trilogies had their third film as their worst rated film. There are two factors that contribute to threequels almost always being the worst films of the series: formula and necessity. Threequels not only have to tell a great story that tops the films before it, but they also need to tie every loose end and somehow bring a satisfying conclusion to the saga. Additionally, because threequels make more than four times their budgets (on average), many threequels are produced solely to make more money, not for narrative reasons.