why mine to break even?
There are a number of coins that will make you a small profit, so I don't buy your story, especially given the hype surrounding Monero. it should not be mined and dumped if miners can mine it at slightly under trade price.
How about because I didn't say they break even? Try reading.
given that the mining is close to break even most miners have to sell to pay their expenses
Furthermore most miners who are only mining at a small profit are going to be selling at least most of whatever coin they mine, especially if they are doing it at any kind of scale and have bills to pay.