1. Most companies are not international, and don't have to deal with verifying the death certificates from 100+ countries.
2. The challenge is that dividing it up would add overhead to Steam support, especially if the estate does try to break up an account into games. Not to mention that there's really no "cash value" on digital games, since there are things like sales, giveaways, bundles, etc.
3. It obviously won't bring them down, but assuming extra work and liability isn't something they'd do our of the goodness of their hearts.
4. We pay to license Steam games and put them in our Steam libraries. This isn't a new idea...it was a criticism of Steam when it was new, and it was why there was so much pushback. If you're buying expensive brand-new games on Steam rather than on a DRM platform (or waiting until the cost lowers enough to be worth getting only a license), then you've been using Steam wrong.

I'm not even defending Steam here. If you want DRM-free games, buy from GOG. Steam has more games, and sometimes lower prices...but you're not buying a game that you own. It was never a secret. Hence why they marketed it as a Steam Library. You can use whatever you want in the library, but you own none of it.