I think it's very common for developers to overestimate the value of their own code. You see this in the video game community, where people are afraid to open-s

I think it's very common for developers to overestimate the value of their own code. You see this in the video game community, where people are afraid to open-source their Minecraft plugin because they think it'll be "stolen". They choose the future where nobody builds on their plugin (and no amount of attribution will ever feel like enough, so there's some level of "theft" felt by the original author). Most open-source projects are not valuable, and even if they are popular, they could be easily replaced in a few days by another programmer. And usually the license doesn't matter, because nobody forks the project anyway, all development is done in a central repository and the project owner signs off on all of it