Because doing so would require twice the cache and execution bandwidth. It is usually better to take the gamble and fetch just one branch. If you don't want to

Because doing so would require twice the cache and execution bandwidth. It is usually better to take the gamble and fetch just one branch. If you don't want to gamble you could stop the current thread and continue with the execution of another thread (if you have simultaneously multithreading/hyper threading). In some cases the compiler may decide to evaluate both paths and then "undo" the path that was wrong. This is very common on VLIW architectures like Itanium which have hardware support for this (predicates), but it can also be done with other instruction sets.