Because fundamentally you can’t correct for the reference frame if you can’t work out if your dealing with chronological or calendrical units. Calendrical units are in a weird liminal space outside of the earth reference frame. We measure the history of most deep space missions by earth reference frame mission elapsed time and do so by keeping a clock on earth and silently keeping records of the vehicle clock.. but on Mars we have a per mission Sol count that brings Mars time into the mix, and I know for a fact a lot of people neglect the barycentric gravity gradient difference between Earth and Mars because for literally 99.9% of things it doesn’t matter… but if you measure a transit of an Astronomical body from instruments on Mars and don’t deal with the relative reference frames your fractions of an arc second are basically pointless false precision.