HTTPS is not a strict improvement over HTTP. Indeed it adds SSL requirements to the client, increases resources needed to access/serve the content, requires to acquire and maintain a certificate, etc.
It's a common practice to offer HTTPS, but you shouldn't think of it as dogma. It's perfectly reasonable to provide both so that people using old terminals (an iPad v1, or an old game console for example) can access the content without technical issues. Or if you want a very low-resources device to access it.
It's all trade-offs and use-cases. One is not a superset of the other.
It's like saying every door should have a lock. No, not every door is improved by adding a lock. Many use-cases are actually not possible with a lock.
Different situations have different tradeoffs, and different people value different things.