That's a big "might" there. I believe they ARE eligible to collect SS, but only if they stay here.
H1B is good for three years. It can be renewed for another three. After that time you either need to have a green card in the system of leave. No guarantees you can stay but must pay FICA taxes anyway.
I think the thing behind F1 not paying them is that the program started as one year of “practical training” so that they can learn to apply what they’ve studied and then take it back to use in their home countries. One year became three, which becomes forever.