If we built a habitable dome on Mars with a breathable atmosphere, Mars would still have a globally inhospitable atmosphere. Our key word "global" does not strictly mean every square inch of available space, but the overwhelming majority, which in this case also heavily impacts the remainder (such as requiring a habitable dome in the Mars example).
> Atmospheric CO2 concentrations (ppm) derived from in situ air measurements at Mauna Loa, Observatory, Hawaii.