People require life support and don't want to spend 80,000 years travelling 4 light years. Automated probes don't have that problem, although they still need to

People require life support and don't want to spend 80,000 years travelling 4 light years. Automated probes don't have that problem, although they still need to last that long in the hostile conditions of space, which is another not-insignificant issue. At the other end, an automated probe could both accelerate and decelerate at significantly higher than 1G if desired. So automated probes have a vastly wider set of possible mission parameters available to them. You can deploy a solar sail to decelerate as you approach another star. This limits how fast you can go as you need sufficient time to decelerate. Additionally, you have drag in interstellar space anyway just from dust and gas particles slowing you down. Fun fact: to accelerate beyond about 0.86-0.9c your ship would need to be aerodynamic because of the decceleration effect of the interstellar medium. What you're really building here is what's often called an "interstellar highway". If fusion ever becomes viable you can extend this to having waypoints to accelerate or decelerate (as required) a spaceship along the path but that's not strictly required. So building such a system will likely take hundreds, possibly thousands, of years but ultimately result in something where you can travel between the endpoints in a few decades.