To some airlines, particularly those in the US, the lounges represent a revenue stream. The lounge itself is expensive to run (just renting the space is expensive!) and AF/KL hardly make money from the lounges; instead they are being used as benefits to C and elite pax.

If paid lounge access results in more revenue for AFKL and it keeps the ticket prices low, I'm for it. Rest assured though, I don't think many people actually pay $30 to spend some time in a lounge. Remember, this is an outstation, so very few pax are connecting there. If it's just a departure point, few people arrive at the airport so far in advance to make the lounge access worth it.

Personally, I arrive at the airport with some time to spare, but I never end up just waiting for too long. I would not pay $30 to spend 40 minutes in a lounge. On a 4 hour connection it would be a different story.