Brake fluid is not flushed due to heat cycling, that is what bleed maintenance is for. Flushing every 2 years is because brake fluid is hygroscopic (absorbs water), and even brake systems are not perfectly sealed. Water in the fluid reduces its effectiveness and can cause rusting in the brake lines, leading to failure.

EVERY vehicle should have brake fluid flushed every 2 years. That Tesla recommends 4 years is straight out incompetent.

That's a useless data point without knowing how much you drive. a taxicab or police vehicle racks up hundreds of thousands of miles per year, and thus needs fluids far more often than every two years.