I think I've heard SQLite creator Richard D Hipp say in the past that he thinks using the public domain declaration rather than a regular open source license was a mistake.

Public domain raises all sorts of challenges for potential adopters of the software that aren't an issue with a more deliberately designed license.

UPDATE: I misremembered this. He does talk about some of the surprise challenges in this interview, but does not go as far as saying that he regretted it: https://changelog.com/podcast/201#transcript-215