A while ago, my last avatar was Sis from Alpha Protocol. Considering that Monolith Productions no longer exists as of yesterday I needed to mourn.
Anyway, to bring this back around to Steam, I've actually sent dozens of emails to Monolith over the past few years begging them to do whatever it takes to get their games on Steam. The problem is that the best ones are owned by either Fox or Sierra, the former of which no longer has any involvement in video games and the latter of which was eaten by Activision a few years ago.
At least Blood, Blood 2 and SHOGO are available on GOG, but I would bet that the No One Lives Forever games would sell like hotcakes on Steam or GOG because they're extremely well regarded by the people who played them, and a lot of people missed out on them.