I have started buying them here and there and noticed the main title song missing on a few soundtracks(noticeably Adele-Skyfall and Sam Smith song on Spectre).

Is that normal for big budget movies not include main title songs on their cd soundtracks.

This happens when the artist performing the song is signed to a different label than one releasing the soundtrack. Fairly new thing not found on older soundtracks. I know the Adele one as available as cd single.

I believe they started this trend with Casino Royale. Strange that the very next movie (Quantum of Solace) featured the main song (Another Way to Die) on the soundtrack CD but then the two soundtracks after it were both missing the main songs.

I wonder if it is a length issue, as the last two albums are close to the 80 minute CD max without the songs, while the QoS CD is only 61 minutes with it. Doesn't explain Casino Royale, though.

I wish the Bond movies had a separate music score track but looks like those are becoming a thing of the past.