Most folks who dive aren't divers. Diving is something they do from time to time. They like it, but they aren't all that excited about it. It's easy to give up or merely forget about.
Some are short time divers. They love diving, but their only diving activity is sightseeing. Before too long, they get bored and drop out.
Others are divers. Diving is their lifestyle. They define themselves as divers. They don't say, "I'm an attorney" or "an accountant" or whatever they do to put food on the table, they say, "I'm a diver." These people have many different diving activities, they sightsee, they take photographs, they hunt for fish and/or bugs, they explore wrecks or caves, they conduct fish counts, they participate in clean ups, they collect fossils, they collect artifacts, they dive for the pure joy of it. They may go through periods of inactivity because of a lack of funds or because kids must take a higher priority, but even when they aren't diving, they are divers, they return to diving as soon and as often as possible.