Patri Friedman asks why websites often require users to deal with annoying pulldown menus such as those listing 50 states. I expect that the main reason is that users who are allowed to type in text will enter it in nonstandard forms. For example, Massachusetts will be entered as Mass or MA, or if limited to 2 characters the user might not remember the correct 2-letter code. Sites that need to calculate sales taxes differently for different state, or who think (not necessarily with good reason) that they need to analyze customers by location for marketing reasons, need either standardized input or a good deal of imagination to predict all variants they will get. Imagination isn’t cheap.
I suspect there’s also a desire by some designers to show their status over users by preventing users from entering unexpected input.
I doubt these factors are enough to explain all examples of annoying pulldown menus, but I’d guess they explain at least half.