Mars is also much lighter than Earth. Venus is less massive than Earth, but not by much.
Even so, Venus has had most of its hydrogen stripped away over time. Thanks to its high temperature, that also includes hydrogens formerly bound in heavier molecules, like water. The process continues, very slowly. Venus is still losing its hydrogen and helium, more quickly than Earth.
One terraforming plan for Venus involves shipping magnesium hydride there, decomposing it, and using both the H2 and the Mg to react with all the CO2 in the atmosphere to make soot, chalk, and water, reducing the surface pressure to about 3 atm of mostly N2. Nothing works without shipping hydrogen to Venus. But once it's there, it will take many millions of years to get stripped away again, because that happens so slowly, over geologic time scales.
Even so, Venus has had most of its hydrogen stripped away over time. Thanks to its high temperature, that also includes hydrogens formerly bound in heavier molecules, like water. The process continues, very slowly. Venus is still losing its hydrogen and helium, more quickly than Earth.
One terraforming plan for Venus involves shipping magnesium hydride there, decomposing it, and using both the H2 and the Mg to react with all the CO2 in the atmosphere to make soot, chalk, and water, reducing the surface pressure to about 3 atm of mostly N2. Nothing works without shipping hydrogen to Venus. But once it's there, it will take many millions of years to get stripped away again, because that happens so slowly, over geologic time scales.