Publishing firms fear writers who self publish for a number of reasons, in my opinion one of the main ones hinges on the fact that they fear the loss of control of the market. To give you an example, if a music producers only allows you to hear Beethoven, how are you supposed to hear about other musicians.
It is the same with writing, publishers will only promote books and writers THEY think will sell -which is understandable - but by the same sword, how can they tell what may sell if they limit your field of reading.
This is why zombie books keep flooding the market, they are a ready sale the same as fanfiction on line.
The new age of writers with internet access and the chance to risk all for their art are rightly seen as a threat to publishing houses; which for too long have told the readers what they want to read.
My views on advances:- If you get lucky and get a publisher interested you may be offered two options a big advance or a smaller one. I would always chose a small one, an advance is a loan for sales to come. Economics 101 a loan needs to be paid back, before you see any money; therefore the smaller the loan, the quicker it's paid and the sooner you may see the money. Another aspect to consider, while we may think our work is good, the bottom line reads it's down to the buyers and if the books don't sell, we are left to pay back the loan out of our pocket and as an indie writer that is going to kill you.