The size of the objects that SpaceX is landing is much larger. The approach that was used here for Perseverance (Skycrane) would not work for larger ships, like those required for a human mission. Just like the previous approaches, e.g. Lithobraking with Spirit and Opportunity, would not have worked for Perseverance.
Larger objects are much more difficult to land. Simply put, while mass will increase by the power of three, surface area, which is used for aerobraking only scales by the power of two, relative to size.
In order to land something large enough to carry and support humans (10-100t), you need hypersonic retropropulsion. Guess who was the first to achieve this? SpaceX. And they remain the only ones. When they light the three engines for the entry burn the earth atmosphere is very similar to the relevant section of the future Mars decent. By developing the first stage landing of Flacon 9, they solved one of the biggest development challenges for humans landing on Mars and it was not by accident. NASA was very happy to get that data and helped them collect it with their chase planes.
