Dairy cows are a different breed from meat cows and, if sold, generally only qualify as the lowest grades of meat. What you’re saying may occur at the individual, artisanal end of the market but generally commodity dairy producers will turn their excess heads into veal. I’ve never heard of commodity dairy producers attempt to make a profit from rearing excess dairy cattle into steers and I suspect the cost of feed + care would make this a loss making venture.
I’ve noticed the past three or four times I’ve been at the grocery store that milk has been consistently cheap lately. Though I wouldn’t expect demand for milk to be very flexible-- Nobody says “Oh, milk is expensive right now, I’ll just put off buying it for another week or two”.
But Heaven forfend the government drive those poor, hard-working, conservative farmers out of business by cutting off subsidies!