This information is outdated and misleading. Since 2020, licenses for public broadcast are only required for broadcasts which, averaged over six months, exceed 20000 viewers and have significant importance for the formation of public and private opinion [1].
Prior to this change, some streamers had indeed been forced to acquire such a license (although there were more conditions than just regularly having 500 viewers). Also, licenses for streamers actually cost around 1000-2500 €, instead of the 10000 € you claimed. In addition, there was an exception for cases where this would be an undue hardship [2]. The regulator basically agreed that this was pretty silly, but that it planned to enforce the law as written (as is its job), until it was changed (which it has been).
[1] (german) § 54 MStV, https://www.gesetze-bayern.de/Content/Document/MStV-54
[2] (german) https://t3n.de/news/livestreams-rundfunklizenz-1175321/