Everybody has different preferences so what may work for one person may not work for someone else. My wallet could testify that indeed many times the monthly and daily deals on Amazon can be found on other sites.
Sometimes it's because it's a publisher discount and sometimes I think that they are price-matching. I'm not a romance or science fiction reader. Mostly I read mysteries and historical fiction. I just don't encounter situations where the only place to buy the books that I like is Amazon or I'd be a Kindle user only and not bother looking at any other sites. Life would be simpler! And, I do agree that many times the B&N site is more expensive on regular priced books than other sites. I buy most books from Sony or Kobo and as a first option check my local library. There is no one answer to everybody's situation. But to answer the OP's original question, there are discounts on B&N but you have to go searching for them.