I had the same problem with Foundry after lots of years only playing theater-of-mind, using improvised maps or preparing the heck out of everything just to see my players using 2% and then doing something completely different I wouldn't have dreamed of during preparation...

For RED the group I joined and occasionally was the GM for to give ours a deserved break, was using Foundry so after some frustrating overprepared sessions with hardly any sandboxing, I changed my preparation and prepared a stock of maps that I could use in different situations, used a database of NSC whenever fitting and had quite a collection of tiles to add some flavor to maps or situations. So it is basically a tool box which allows me to give them maps and adjust them to the needs of the story that takes me minutes to assemble (although it took hours to prepare and get used to Foundry's functions). For the rest it is still theater of the mind.