Releasing the Dig Tool for Career/Story mode is something the community has been asking for since not long after the game's release. I suspect we haven't got it because FD doesn't want to remove those invisible and non-interactive walls they're so fond of using (or make a tool that lets us do it).

Did you know that the 7-11 next to the Ramen shop can be renovated to a small, single level, 2-bedroom town house because they forget to put an invisible wall in front of the false double door on the wall facing the canal? You can grab the false door from the wall, sell it, and replace it with a working door that gives you access to that side of the block.

Honestly, I just don't see the point of restricting the career/story mode houses the way they do. Some of us have no interest in playing Sandbox mode to get full functionality. And for houses that do have exisiting basements, not being able to expand them to better use the space is frustrating (thinking of you, Amusement Park and my dashed dreams of an underground parking garage/storage units).