Most agents accept less than 1 percent of submissions. Editors tell me that they toss back at least ninety manuscripts for every one they buy.
Just sending to more publishers isn’t the answer. Even if fifty-three editors see the same badly written piece, the answer will be the same. Instead, if you have sent out a piece at least a dozen times and everyone rejects it, assume that you need to re-work the material before you send it again. At least get a professional to evaluate it.
Today we also have to admit that some people are published because they can sell. If they would put a fourth of the effort into writing that they do into selling, they could develop into excellent writers. They use their sales figures as proof that they're good writers.
Some poor writers sell many books. That doesn't make them good writers. It means they are inferior writers who know how to sell inferior books.