Are you sure you are not just projecting your own insecurities and opinions into interviewers? Majority of developers don't have side projects. According to FOSS survey, owerwhelming majority of linux (especially) and open source contributions is paid work. Sometimes it is that they work so much in day job, most of the time they work normally (which is enough) and do other things in out of work time (exercise, care about children, read books, socialize - social skill matters, craft). If you are coding 6 hours a day (generous 2 hours for meetings and chatting and organizing), then you should code plenty.
You could have loose that interview due to many other reasons, you could have run into that one company that does not hire without outside code.
But if you really worry about this one, maybe create an account with sample project and be open about that project purpose (e.g. dont be afraid to say that you created this project to show how I code, because previous interviewers asked for that). If it is really about code sample, then something you create withing two days should suffice.
And if they demand real contributions to real open source projects, ask them whether their company gives employees time to do such a thing on the clock. After all, they expect your previous employers to be so generous with time, so they should put money where their mouths are. If you dont hire me without having full public profile, it is only fair to demand that being employed by you makes continuing that work possible.