Most people here start hobby around high school or university, but before publishers started to recognize that most people can't really drop 1/3 of their scholarship on one book and made some steps to reduce the cost… people had two options. Don't play or make own setting. According to my father and brother, in the '90s you could bet that most groups had one or two books and at least one collaborative home-brew setting or system. After all, you can pin-point a fantasy or sci-fi book that your group likes and make a setting together for a cost of few nights worth of coffee… significantly less than hardcover RPG ;). Hell, there were at least six versions of Witcher RPG before even the Polish book series was completed (around 1997 iirc).
A lot of the modern Polish authors started by getting recognized as particularly prolific people on Polish parts of usenet, IRC or fora. There is still a magazine called "Tawerna RPG" ("RPG Inn" would be best translation) that started their distribution around 1996 via one CD-ROM gaming magazine, they had a part of their CDs dedicated to readers creations. Games, magazines, long-form blogs etc. I'm not even sure if that magazine still exists, but Tawerna prevailed ;).
It's actually a bit sad that many people choose to buy books instead of making their own materials. It seemed almost like a honed tradition until less than a decade ago.
But it's not exclusive to Poland. Germany had similar, if somewhat less prolific scene. Sweden almost relishes in gaming exclusively the Swedish RPGs. Reasons were similar to Polish: a lot of the books were insultingly expensive while having pathetic amount of printed copies. Right now D&D is not the most popular game, or even considered as gateway drug, in any of the countries that I have mentioned.