Why were players never told about the little tricks of the trade we could employ in the instructions book, such as force-moving Riflemen to make them run faster, or how to use Grid Smashers coupled with Artillery Designators?

Why were all of these details not even told to us afterwards?

most games won't come with a complete instruction set. For most games, you get basic controls and how to play, but advanced play will come from experiance.

i see that

i also remember when instructions books used to be very detailed

this is when a downloadable PDF for your computer comes into play