Almost none of the games pictured are actually "doujin" games - they are commercial publishers.
Also, the reason we don't remember PC-98 is because it was never sold in the US (except for the very unpopular APC-III). It was the most popular computer on Japan from late 80s to early 90s and is well remembered there. Being the most popular PC, there is a huge amount of software for it, including huge amounts of office and productivity software, many genres of games, and plenty of Western ports.
Also, the reason we don't remember PC-98 is because it was never sold in the US (except for the very unpopular APC-III). It was the most popular computer on Japan from late 80s to early 90s and is well remembered there. Being the most popular PC, there is a huge amount of software for it, including huge amounts of office and productivity software, many genres of games, and plenty of Western ports.