General knowledge, FOSS, and learning material are also generally freely given without expectation of or often even asking for compensation. The most valuable "content" on the web is generally not monetized[0].
They wouldn't be losing a lot if they lost out on TikTok and Instagram. It would be no great loss if affiliate link blog spam went away.
[0] e.g. https://axler.net/ has multiple free books on advanced mathematics written by a well-regarded author. This kind of thing (and/or lecture notes, syllabi, and homework) is not at all abnormal to find on professors' home pages if you want a free education.
They wouldn't be losing a lot if they lost out on TikTok and Instagram. It would be no great loss if affiliate link blog spam went away.
[0] e.g. https://axler.net/ has multiple free books on advanced mathematics written by a well-regarded author. This kind of thing (and/or lecture notes, syllabi, and homework) is not at all abnormal to find on professors' home pages if you want a free education.