That’s fine. And driving the speed limit in any lane is never against the law. Neither is going slow in a self-check out lane or leaving a cart in a parking spot at the grocery store. There are things we do as citizens that are conscientious of others. The law is not the issue.
In many states, there are hours of HOV lane usage (rush hour). When outside those hours, the lane just simply converts to a typical left lane. This again highlights the purpose of the lane.