Neither Venus nor Mercury have substantial magnetic fields presently (compared to Earth).

I don’t know enough to know if that supports the GP’s conclusion or not, but it may.

These are pretty well researched, observed, and understood subjects. https://en.wikipedia.org/wiki/Atmosphere_of_Venus explains it quite well, particular https://en.wikipedia.org/wiki/Atmosphere_of_Venus#Induced_ma... which explains how Venus is currently losing its atmosphere in the way described above. And https://en.wikipedia.org/wiki/Atmosphere_of_Mercury: "The Mercurian exosphere consists of a variety of species originating either from the Solar wind or from the planetary crust [...] This corresponds to a surface pressure of less than 10^-14 bar (1 nPa)" which is about 1% of what is considered "ultra-high vacuum" (https://en.wikipedia.org/wiki/Orders_of_magnitude_(pressure))

Mercury has no magnetic field, and no meaningful atmosphere like we'd understand it. Venus has a minimal magnetic field, and is covered in hot dense CO2 layer because the solar wind blew away all the hydrogen and continues to blow away the atmosphere. The Earth has a much stronger magnetic field that has protected our oxidized hydrogen, and good evidence points to the giant impact hypothesis.