Welcome to the forums.
Why use a reseller?
The only resons I can think of are:
Impulse buying: Vendor has a booth etc, at the mall, and the wavering customer decides then and there to go with sat service.
Keeping $$ local: Signs up with the local mom and pop video service with the D* newspaper or print add to keep them in business by keeping the $$ local.
Service reputation: Local vendor has a great service record in their respective market. Friends or neighbors talk about what a great ontime no hassle installation they had done at their home.
Promised a "great deal" on free programming during the personal (not to an 800 number from ????) phone call to a local number. Liked the sound of that compared to cold calling D* and playing CSR roulette.
Four quick ones I could come up with but I just called the 800 number at the time I had my initial install completed.
Like you I did the research online, for programming, pricing, and hardware requirements and/or availability before I took the plunge.