I don't use visual studio, so I've no idea what it is you want to do with it. You can export your files and open them in any editor and edit the code and there will be a few programs/apps that you will be able to open them and manipulate them visually as well. What you won't be able to do though, once you edit them outside of BSS, is import them back in and still have full visual drag/drop capability.
What is it you want to do with the site within Visual Studio. That may help others to know if you can do it or not.
I use Visual Studio for data interactions with SQL Server. It's literally drag and drop stuff to connect with and .net code to manage logic, stored procedures, etc.
But I couldn't figure out Bootstrap actually IN Visual Studio, So I used Bootstrap Studio to mock up the site thinking that I could then import into VS and have it become a full fledged visual studio project automatically.
Short answer, to take advantage of Visual Studio's .net coding and data integration with SQL Server