Not following what you are saying. Airlines are required to include all mandated taxes and fees in their advertised fares. They clearly say the $59 price is the one-way fare, not round-trip. I priced out one of their $59 one-way fares and it included all taxes and fees. Booking a roundtrip gave a $118 price that was inclusive of all taxes and fees. The $4 seat fee is an option and not required to be included in the price.
Basically I'm saying they did what they were required to, just that the presentation was confusing.