It's not just discourage as you think, it's forbidding in some scenario. If a merchant use a fix address to receive payment , it can only receive 6 payments per hour. Basically makes the service useless. It's customers have to wait forever if there're more than 6 payments per hour.
What merchant uses a static address for all customers? Horribly insecure and prone to problems. Anyone that foolish should just use a service like bitpay and have it done right by someone competent.
The moment a business realises someone can look up their address and see their takings... they will want to use unique-addresses at checkout afterall...