That's because that's not what social media is FOR. You are doing it wrong.
It's like, if you were presented with your choice of every restaurant & every type of cuisine in the world, still only ever picking McDonalds and then complaining that IT'S ALL JUNK FOOD. You make your twitter feed... it is the way it is because you select the people and voices to make it that way. Aaaaand you pretty much just admitted that you do the exact same thing. This is the twitter experience you chose; it is NOT the only experience there can be.
Or what Max said:
A lot of people on twitter take the "social" seriously. It's about
community. They aren't there to be a customer base, or an audience for drive-by self-promotion, and a lot of us find it outright offensive that people are pushing it as a platform to sell on. Yes, there are small publishers and self-declared experts who tell you to tout your wares all over social media, but IMNSHO that's a truly terrible suggestion. There are people who I genuinely liked, but not only have stopped following, but whose books I won't *ever* buy just because they were too about the hard sell. I know I'm far from alone in that. By way of analogy, picture being invited over to a friend's house to hang out with a bunch of people and maybe watch a game, or play cards, or something, and as soon as everyone is there and the party's just starting pulling out a credit card machine and a box of things to sell them, and talking over everyone else until they either buy something, leave, or kick you out. It's crass behavior, it's ineffective, and it makes people not want to interact with you. It makes whatever actually interesting things you might have to contribute to the larger conversation not worth the effort to wait for.
There are a LOT of writers on twitter, and a lot of other people in the field, and many of them have lots of funny, intelligent, interesting, helpful things to say. And by being themselves, and being part of the larger conversation, they win far more fans (and sales) than the disruptive me-me-me pitches ever will. And I'm sure there's someone who will say I'm wrong and they've sold a bazillion copies of something by being relentlessly obnoxious at people online, but I don't think any of us should want to be that person. At least I sure don't.
What I can say is that by being on twitter just to participate in the conversations, I have made great friends, I have learned incredible things that have helped me with writing (and art, and fixing stuff, and you name it), have had the opportunity to listen to the voices of people who have vastly expanded my world view and my understanding of my fellow human beings in it. It's invaluable to me as a human being, and even more so as a writer. And yeah, incidentally, it's helped me get readers too.
Yes! Also, one of our AW occasional regulars has a site where she collects the wish list tweets:
http://mswishlist.com/