Probably 80+ % of large corporation web apps are java, plus they have a large base of C and C++ windows people around who are also used to working in an object-oriented environment. C# more closely resembles those languages.
Later versions of VB had some OO type capabilities, but it was limited. It also was excluded from parts of the windows api, mostly due to data-typing/marshaling issues that could be handled by the C community. Going from serial event-based programming with some OO capability into a full OO environment is a mindset leap for how you think about programming and design.
IMHO, the people who first appreciated the extent to which you could take .net came from the java/C community rather than the VB community and they opted to go with their background and picked up on C#.
Personally, I like VB.net better because it tends to be a little more self-documenting. Only thing I haven't been able to do in VB.net that I could do in C#.net was to use pointers - but that may be due more to my lack of knowledge that deficiencies of the language.
What I'd really like to see is the ability to use more than one language in a project and the results compiled into one dll.