When looking through challenges, I noticed that some series of challenges feel incomplete. For example, the GTA series has a challenge for the 2D and 3D eras, but not one for the HD era. Likewise, there is no "Snaaaaaakeeee!" volume 4 containing MGS4, PW and V.

Is there a specific reason for there not being challenges like this? Would be cool to have the complete set.

The only specific reason is time...or lack thereof

I thought so, thanks for elaborating :)
And sorry if the post feels a bit redundant