Resources that are "Unlimited" in marketing speak are rate-limited in practice. Your unlimited internet connection limits your daily transfer by bandwidth, both at your port and at the remote service ports. Your daily amount of SMS is limited by sending rate. Your all-you-can-eat restaurant order is limited by your belly.

No wonder that access to an expensive API which is an LLM is also rate-limited.

What does surprise me is that you can't buy an extra serving by paying more (twice the limit for 3x the cost, for instance). Either subscriptions don't make enough money, or their limits are at their datacenters and they have no spare capacity for premium plans.