What people don't realise is that Gemini is a different thing for each person involved with the ecosystem. Some people are in it because it is easy to implement, something that can't be said about the recent specs of HTTP/HTML specs. Others enjoy having a spec that is easy to understand and absorb, even if they're not developing with it. There are those that like how clients decide how to present the content, and that some clients allow for a ton of customisation thus placing the user in control of the presentation. Each person is enjoying the ecosystem for their own reason, and that doesn't need to be a reason that serves as an answer to "why not HTML and HTTP?"
Mostly, people do Gemini stuff because they're having fun, and that is enough.
Lagrange is a great client. There are a gazilion others. Pick one up for a ride, have fun.