I don't think these cables are a good example of a public good. They are eminently excludable; you can't transmit data on the cable if the owner doesn't let you, and it is easy to tell who is transmitting since they have to ask permission. The fact that most are built and owned by private companies who invest then collect the revenues seem to mark it as a standard high upfront cost industry.
They are also rivalrous, as your example of Google et al. building their own demonstrates, although at this point they are not so much rivalrous to individuals as they are for large data moving companies due to their huge capacity.
I don't think these cables are a good example of a public good. They are eminently excludable; you can't transmit data on the cable if the owner doesn't let you, and it is easy to tell who is transmitting since they have to ask permission. The fact that most are built and owned by private companies who invest then collect the revenues seem to mark it as a standard high upfront cost industry.
They are also rivalrous, as your example of Google et al. building their own demonstrates, although at this point they are not so much rivalrous to individuals as they are for large data moving companies due to their huge capacity.