A modern processor pipeline is dozens of cycles deep. Without branch prediction, we would need to know the next instruction at all times before beginning to fetch it. So we couldn’t begin fetching anything until the current instruction is decoded and we know it’s not a branch or jump. Even more seriously, if it is a branch, we would need to stall the pipeline and not do anything until the instruction finishes executing and we know whether it’s taken or not (possibly dozens of cycles later, or hundreds if it depends on a memory access). Stalling for so many cycles on every branch is totally incompatible with any kind of modern performance. If you want a processor that works this way, buy a microcontroller.