BC = typo for CB, i think. Anyway, here's my personal interpretation for why we use wxWidgets instead of QT.
wxWidgets is portable to many platforms, and it uses the platform's native widgets when possible, which makes a good cross-platform implementation, at least for Windows. Windows users shouldn't be asked to install X, Y or Z widget library separately before installing a program - and when they do, the end result isn't exactly pretty. I believe that choosing wxWidgets as the widget library was a key factor in making C::B a success.
That, and considering that in its beginnings, C::B was a Windows-only program, wxWidgets was the only practical choice.