An open source license is a grant from the copyright holder to someone else, giving them additional rights. If I give you the rights to version 2 of my work, I don't have to give you rights to use version 3 of my work, because it's mine. If version 2 is GPL, version 3 can be BSD licensed, closed source, or only available to Martians, that's up to me.
Now, if I have code in my work that belongs to other people that they have given to me under the GPL, I can't unilaterally change the license, because that would involve someone else's stuff. But other licenses, such as BSD, would allow that.
The concept of Copyleft is relevant to your question - for non copyleft or permissive open source licenses, the fact that a derived work can disappear behind a closed source license is considered to be a feature, not a bug.
Both sets of free software licences offer the same freedoms in terms of how the software can be used, studied, and privately modified. A major difference is that when the software is being redistributed (either modified or unmodified), permissive licences permit the redistributor to restrict access to the modified source code, while copyleft licenses do not allow this restriction.