Many current outlines for trips to mars, such as Mars Base Camp, propose a large ship capable of transporting astronauts to Mars. However this plan only proposes to send humans to Mars' orbit and not the surface. So what is the purpose of a manned flyby/orbit of Mars but not actually landing on the surface? It seems like a ton of infrastructure just to do something that can be done by robotic probes fairly easily.
The wikipedia article on Mars Base Camp describes its purposes. Lightweight robots can be operated by humans from orbit with only milliseconds of latency, as compared with the several minutes of latency they'd have if controlled from Earth; MBC can also be used as a staging area for Phobos/Deimos missions.
As @called2voyage points out, Mars landing and return is a significantly greater challenge than reaching Mars orbit; you have to give up about 13 kg of payload in Mars orbit for each kg of payload you want to land and return to orbit. Sending robots on one-way trips without the additional mass of life support equipment is one way to minimize this penalty.
Finally, it's worth noting that Lockheed Martin doesn't have a space program; their goal with the Mars Base Camp proposal is to sell hardware to NASA.