I think the smaller character limit comes in from Asian countries if they don’t use the basic Latin characters that came out of ASCII. But yes, there’s no reason for the service provider not to offer unlimited SMS messages other than greed/lack of competition. I remember over 20 years ago reading a high level phone company employee talking about how the SMS plans were basically printing money for the phone companies because it cost them almost nothing in terms of bandwidth, utilizing an otherwise unused part of the connection protocol. Back then most companies charged for the messages as in @OP’s question, and the plans were relatively expensive. Nowadays most plans I see in the US and Europe offer unlimited talk and text, or limits that are so high they would be hard to reach. I think it’s a combination of competition and smart phones offering SMS alternatives that offer more functionality while using a tiny fraction of your data allowance, or none if you’re on WiFi.