Should be added that the malicious part is often done by a third party that takes over an open source project when the original developer doesn't have the time/energy/money to maintain their open source/free work. Many Chrome extensions end up being sold for thousands or just hundreds of dollars because there's no money in them and the dev isn't all that interested.

Society as a whole could easily avoid this by funding open source/free utilities to the point where malware makers need to spend significant cash to outbid yearly community support, but unfortunately maintaining anything available online for free is a thankless job that barely covers the electricity required to maintain the code.

In this case too, the developers behind the theme seemed to want to monetise their work, which had attained almost 4 million installs, in the past, but found themselves with a rather unwilling customer base. I don't know if they snapped and uploaded something malicious or if they're intentionally making it hard for forks to copy their work, but either way the lesson learned is that if you want to make money you should just abandon your free projects and start something else.