For example, the people who work there usually choose what single to release, because they’re expecting which ones would hit #1, sell more on iTunes, etc.

I think it’s an exaggeration when people say that the major record labels are dictators of artistic freedom, but they do have a lot of the say in what artists do in their label.

In independent music labels, you’re not guaranteed to be on MTV or be on the radio, so there is more artistic freedom in what you can put on a record and what you want your sound to sound like despite what the public would think of it.

A lot of artists/bands would switch from independent to major, and so I’m guessing that fans would compare their old music (independent) to their new music (major) and say that the artist/band sold out if the music is completely different. Because they’re signed to a major record label, fans would assume that the label gets to decide what sounds more fresh.

I personally think it’s a stereotype, because that does not happen to every artist that switches off. I also think "sell-out" is being thrown around too often that the meaning of the word doesn’t mean anything anymore. I wonder how people could possibly know why bands would change their music and why they would assume it’s always about money.
References :