The problem comes when one assumes someone with a binder full of pirated games would otherwise have a binder full of legitimate games. Pirating is likely their hobby. If they couldn't pirate Dreamcast games they would just pirate something else. What they likely wouldn't do is turn into a legitimate collector if pirating weren't an option. These people got into pirating because they were cheapskates.
And Dreamcast game pirating, while it had a very visible scene, was not something a common user would do.
It's not so cut and dry. Yes, there are some people who never pay for anything and only pirate something. But for most people it just depends on what's easily available. See e.g. movie and music streaming services being successful today, despite widespread piracy 20-25 years ago.
In the case of Dreamcast pirates, while I'm sure they wouldn't pay for every game or even most games, many of these folks would very likely purchase some games, had pirated copies not been ridiculously easily available for free.
In the specific case of the person I knew, he had purchased games for plenty of other consoles.
And Dreamcast game pirating, while it had a very visible scene, was not something a common user would do.