Apparently the "Taproot" Bitcoin update made it easier to upload image-sized data once again, which had become prohibitively expensive 2023 and much earlier:
Developer Casey Rodarmor apparently contributed to this popularization.
- ordinals.com/ appears to index some types of ordinals
This in turn led to a lot of child porn rediscussion, and people linking back to this page to view earlier inscriptions: incoming links.
TODO understand this new system in detail.