Why no nominations for "Shameless"?

I agree, but the show is ignored largely by most awards bodies because it doesn't fit neatly into comedy or drama. William H Macy has done well since it was moved to comedy since his role is generally comic. Emmy has some comedy in her role, but it's primarily dramatic. She has been nommed for some smaller awards though:
2012 Critics' Choice Television Award Best Actress in a Drama Series
2012 PRISM Performance in a Comedy Series
2013 Golden Europe Television Award Outstanding Lead Actress – Drama
2014 Critics' Choice Television Award Best Actress in a Comedy Series
2015 Satellite Awards Best Actress in a Comedy Series
Notice that different organizations put the show in different categories. I think one of the reasons she hasn't won any of these awards is that they tend to go to performances that fit more neatly into the comedy or drama category.

I totally agree. Her performance over the past four seasons has been incredible. I can't imagine how much energy and dedication it takes to keep that level of quality. She definitely deserves awards for her portrayal of Fiona and it really saddens me that she hasn't gotten her due from the major awards yet.

I tend to agree with funnygurl, that it's probably in large part due to the fact that it's difficult to classify Shameless as either a drama or a comedy. With so many shows now being a mix of the two, the rigid classification does seem antiquated. I also think that, maybe mostly in the early seasons before it really gained the level of public awareness that it has now, the no-holds-barred and very unglamorous look at what life is like for families like the Gallaghers maybe was a bit much for people to handle - despite the fact that the show has always handled it's subject matter extremely well. Poverty, all kinds of abuse, mental illness, realistic sexuality, etc., isn't really things that people were super eager to deal with.

Luckily though, people are starting to see that Shameless really is very high quality television, both regarding the acting, writing, production, etc. and the show has actually always been well-liked by critics. I hope that it means that there will be more awards-recognition for the show in the future, but I really don't know. I think there needs to be some shifts in regards to how shows are classified for that to happen.
There are many shows that are in that same predicament - neither fully comedy or drama. Orange Is The New Black is another example of this.

William H. Macy just won a SAG Award for Frank, and before the awards he talked to Variety and said this, which I think ties in nicely with what I wrote the other day:

Before the awards, Macy told Variety, “There’s some sort of critical mass moving on ‘Shameless.’ It’s bold and bodacious and pushes the boundaries of good taste. But the audience numbers are getting up there that now award personnel and critics and media people are taking notice.”
Source: http://variety.com/2015/tv/news/sag-awards-newcomers-reign-in-tv-races -1201414816/

I agree! Love her and love the show!