Just wanted to ask why are those titles not on GOG yet? Are there any problems?

Probably half the threads here have something to do with LucasArts not being on GOG, dude. LucasArts wasn't gonna budge, and now that they're owned by Disney we're not sure if they'll budge either. That Full Throttle and Grim Fandango aren't even on Steam is itself puzzling considering the other LA titles they have on there.

I don't know about Bloodlines but I think it may have something to do with the fact it was made with the Source engine. Not sure if Valve would be too permissive about a Source game being sold through a means outside of Steam, even if both the publisher and developer are on board with GOG.

Dear Esther runs on the Source engine, as far as I know, and it's sold outside of Steam.

Bloodlines was available at DotEmu for a long time, though for 20$, i.e. outside of GOG's two only price points (at that time). It was available from other shops as well, but has been removed from everywhere except Steam. No official reason has been given. Speculations range from a Steam-exclusive deal to licensing problems (the music in particular might be causing trouble).

Activision gonna Activision.

This is very sad, there are quite a few games without which no one can call their collection complete. I imagine there must either be very serious issues or no will at all from the LucasArts/Valve if such classics aren`t yet here.

I know it's sold on online shops that sell Steam keys... has it been released, say, DRM-free? I know it was part of a past Humble Bundle, was it then?

I dunno, what exactly are Valve's rules regarding distributing games using the Source engine anyway? Someone here ought to know more than I do about this matter.

As far as I know, it was before Humble Bundle. You could buy it DRM free from the developer's homepage.