I tend to assume that there’s two reasons. The first, as the second quote shows “Why Not?”. If there’s anyone left who wants to buy one, they’re almost certainly doing so for non-economic/non-need reasons, so why charge more.
The second, is if he keeps mandating the purchase of his vehicles by his other companies, he can continue to artificially increase the value of the Cybertruck to his shareholders and the public, propping up his own ego.
Win/win for Musk.