Does evolution even predict that it would have been practically weeded out? As far as I know we don't even know what causes people to be gay. Some things can't

Does evolution even predict that it would have been practically weeded out? As far as I know we don't even know what causes people to be gay. Some things can't be weeded out by evolution, e.g. we will never lose major traits that are developed in the first weeks of an embryo's development, as everything that develops in the later stages depend on the first. Non-hereditary traits aren't obviously weeded out either, and I don't think homosexuality is (always) hereditary. Has there really been any research by evolutionist biologists suggesting that homosexuality should have been weeded out and it's an anomaly in our theories?