I'm not sure what exactly you want to know. If you're asking why the number of merchants and suppliers that accept bitcoin would increase, it would be because there is profit in it. It adds another source of revenues for the company, and setting it up is very easy.
As the number of things one can buy with them increases, the percentage of bitcoin profits that merchants will cash-out immediately will decrease, as they will become more useful for commerce.
The ideal state is to have a closed economy using bitcoin, which allows people to avoid the inefficiencies of physical currencies.