John Paul Jones (the famous privateer from the American Revolution, not the singer in the '60s rock band) said, "If you do not risk, you cannot win." Sometimes the change in artist brings in more readers than it loses. Sometimes the new style isn't accepted, and the book suffers. This risk is what the comic industry (the people who don't actually write, draw, ink letter or color the books), play with every time they change artists.
Normally the new style created by a new regular artist is eventually accepted by readers and life goes on. This acceptance by some readers is because they know that if they really like the book's characters and storyline they have to get used to the change in art if they want to be faithful. It is kind of a fatalist view of comics. Other readers don't really care too much about the art, just the story. And still other readers actually like the change in artists.
The change in artist that causes the most dissatisfaction in readers is the "guest artist." The regular artist sometimes gets overburdened, or will be given the chance to apply his style to another book. This results in someone else must pulling "art duty" for the book. This change is all well and good for the two artists. The regular artist gets to be creative in another book, and the guest artist (many times someone who doesn't have a regular book, or has a book that is not as popular), gets to show a different audience his style. Unfortunately, the readers have to put up with change. I'd like to think that I'm progressive in my thoughts, but I've found that it doesn't apply to this aspect of comic art. I get attached to the way my favorite characters appear on paper, and don't want them to change (too much). I'll accept a change in regular artist (albeit begrudgingly at first), but it is annoying to see one or two issues by a guest artist, then back to the regular artist, then back to another guest artist, and finally back to the regular artist just to have the editor say that in two issues the regular artist will be moving on to greener pastures. If readers don't like the guest artist they have to wade through an issue with "bad," or "different" art before the "A" team returns in a month or two.. If readers like the guest artist they live with the knowledge that the artist will be leaving in an issue or two, which results in disappointment.
Editors welcome readers to voice their opinions about all aspects of the comics they read. Often opinions, negative as well as positive end up in the letter column of the book about which they are writing. Enough readers indicating dissatisfaction with a particular artist may make a difference in how the book is created. There is one thing to remember, and that is the comic book industry is a business, therefore it follows the number one rule of all businesses. That rule is to make money. Without a profit no company will not stay in business very long (this doesn't apply to the federal government since it is not a business). Artists work for the company, and if there is a monetary reason to make a change in artists then it will be done. Hopefully, most of the time the reason for changing artists is for the benefit of the readers or at least the artist, and not just for a greater profit (I'm sure there is a Rule of Acquisition number covering this, but I don't know what it is).
The bottom line is to read comics that are fun and interesting. If a book doesn't fulfill your wants, then change books. Fortunately for readers, there is a tremendous number of books on the market from which to choose. Each book has its own creative team with its own ideas and direction. Try another book to see if it can fill the void left by a former favorite, you might be pleasantly surprised.
If you don't risk, you cannot win.