A big issue is that neither seem to have developed photosynthetic life[1] and without a lot of oxygen in the atmosphere they don't have an ozone layer. That means that UV light penetrates further and breaks up water into its constituent parts allowing the light hydrogen to be blown away by the solar wind over geological time scales.
[1] It's looking increasingly plausible that Mars developed primitive life, but I'd bet heavily against photosynthesis. That took way longer than chemosynthetic life on Earth.
I think the article speaks to the point you're making also, that the UV light may have been an important (if not primary) mechanism for blasting away Venus' water. So even if someone snapped their fingers and made Venus perfectly terraformed, it probably once again would begin the process of losing its water. And any life would have to survive a brighter sun.