Why are there so many characters?

         In the Merchant of Venice by William Shakespeare, there are a lot of characters. There are a few small ones like Tubal and Old Gobbo, but there are also a lot of big characters, like Salario, Salanio, and a few other of Antonio's friends, that do not seem like they are that important to the story. My question is Why did Shakespeare write all these big parts in his play? I think that one of the main reasons is to make the main characters seem more real, for example, in real life, Antonio would probably have a lot of friends like he did in the play, and Portia would have maids like she did in the play. I think this reality could be achieved without all Antonio's friends being such big parts. If most of them showed up a couple times in the play, but were not huge parts, it would not change the play very much, and it would make it much more clear to the audience. Another reason Shakespeare might have written all these characters as big parts is because he wanted it to be a complicated and interesting story, but I think he has enough interesting plot lines going on in the play, that he could have achieved this complicated play with a few less seemingly unimportant characters.
          These characters may only seem unimportant to me, because I am sure Shakespeare had a reason to write them all, I think it would be helpful to me, and other audiences if he had written a little more about them to show their importance.