If someone finds a way to monetize tweets that's more effective than Twitter's, then Twitter would have an incentive to copy it, therefore competing with its customers.
Long story short, that's the reason Google stopped selling white label search via its api to customers like Yahoo ten years ago.
There are many uses for twitter data outside of just repeating the tweets with a different design. There are quite a few Twitter apps that generate revenue and some have also been acquired by bigger companies. Twitter and Google main service offering are not comparable, since Twitter has the actual data while Google is a gateway.
"we will require you to work with us directly if you believe your application will need more than one million individual user tokens"
which sounds like "show us the money" to me. You can of course assert that "we want to talk to you" obviously means "we don't want to talk to you", but once you do so without evidence you're firmly in tinfoil hat territory.