I'm not an engineer, but it's probably a combination of mission specs being drawn in 2001 and the fact that adapting technology for use in space is a multi-year

I'm not an engineer, but it's probably a combination of mission specs being drawn in 2001 and the fact that adapting technology for use in space is a multi-year process. The Curiosity rover, which was commissioned in 2004 and launched in 2011, has a primary camera with 1600x1200 resolution.