The time is The Future. Humanity is spreading throughout the stars, aided by the invention of Schwarzschild gates.
The gates allow for FTL travel by tearing open wormholes in space. There are three kinds of Schwarzschild gate (and three corresponding modes of operation):
1. Tethered (AKA stable): A 'gate complex' (A mechanism the size of a small city) exists at each end. It draws constant power but maintains an open gate through which people and materials can move freely and bidirectionally to/from a similar gate complex elsewhere in the cosmos. This kind of gate needs a finely calibrated and tuned gate complex to connect to.
2. Captured (AKA Unstable-Bound): A gate complex can open an unstable and very small wormhole, then push a discrete packet of materials or people in a warped bubble of spacetime to a 'receiving complex' (A mechanism the size of a football stadium) at the other end. Travel is unidirectional and takes an immense amount of power which the receiving station is designed to absorb, but bidirectional communication can happen unreliably and at a low bandwidth (due to the error correction data needed). This kind of gate can't establish a lock if no receiving station is present.
3. Directed (AKA Unstable-Unbound. AKA Tunnels of Terror. AKA Brownpant Singularities): A gate complex can temporarily open an unstable wormhole and blast a packet of warped space across the cosmos with sufficient accuracy that it will arrive at a distant planet. Upon arrival the packet will 'pop', delivering a huge burst of high energy plasma (and whatever it's payload was) to a location somewhere on the surface of the planet. This kind of gate doesn't need anything on the distant world, but will level a large amount of real estate somewhere on the planet.
The Human Exploration Core (AKA HEC) has a fairly simple protocol for spreading humanity through the stars. Use a Directed wormhole to throw a collection of automated systems at a distant planet and wait until they build a receiving complex, pinging every so often with a Captured wormhole attempt to see if one has been established. Once one has they will see what is needed at the other end before throwing more colonists and materials at the world until they can build a full gate complex and add the world to the United Federation of Man.
But as everybody knows: Automated systems can't be trusted and the environment at the other end of the wormhole might call for some human ingenuity. So instead of throwing a fully automated device through the Directed wormhole H.E.C instead sends Hazardous Environment Mobile Utility Units (AKA HE-MUUs. AKA Bulls), which are essentially gargantuan, armoured, water and airtight rolling/floating and awe inspiring factories. A HE-MUU is a reconfigurable mining rig, refinery, processing plant and drone operating facility capable of bootstrapping a planet from nothing but bare rock all the way up to having a Gate Complex of it's very own (it takes about five years on average to build a Receiving Complex, then a further four for the full Gate Complex). They can build and maintain automated mines, factories and industrial complexes as needed for the particular planet, they have internal environmental systems that can keep people alive for as long as their lives are without maintenance, they have an AI that stops short of sentience but contains the sum of human knowledge and is insanely good at resource optimisation, and they have one driver.
The question is why only one driver? Given the expense of a HE-MUU (enough to make even a department of the interstellar government think twice) and the energy cost of the wormhole, why would HEC stake the success of an initial colonisation run on one man instead of a whole crew?
A quick note: While writing this question I came up with a few possible answers, but I thought I'd ask it anyway because it was fun to think about. I'm going to be rating answers primarily on how much they would force a one-man-show, since that's the major plot point that needs addressing.