When I did my ow course it was just I did not have to lie anymore when I would dive abroad. I never had problems that 'I had forgotten my cert' , but it looked better to me to do a course after years of some holiday diving (1 day per holiday). And then during my ow course I saw people with a twinset and drysuit. Why is that? They go deep. That is not interesting my instructor said. Oh, I want to go deep. Since then I knew I wanted to do technical diving.
I did my first course with IADS, but before the last dive of the course I had done some dives on my own. Instructor wanted me to wait for AOW till next year, but I did not agree, so moved over to cmas club. But that club was too slow with 2*, I would not have that 2* cert before winter and I wanted to do icediving, so I did a padi aow course.
So I never did a 20th dive on the name of iads, my agency where I started with. My ow instructor called me 10 months later as he heard that I was doing night dives and deep dives and he told me he did not agree. I told him I am already DM and have over 200 dives now. So I was not average, but he did not know I was diving a lot.I have certs from different agencies.
So you cannot know when and if people will do 20 dives in their live, in 1 week, in 2 months or never. Sometimes there are divers you dive with after a course, some you will never see again. I had a student who quited diving after finishing normoxic trimix. And another quit during the course as he needed some more time to practise skills, but he was not interested in diving anymore. I have seen divers quit diving after 2000 dives and some quit during the ow course (seen in cmas clubs a lot not on paid courses).