Shocking price I paid to fly between Bloemfontein & Johannesburg

On 13 October 2022 I was scheduled to fly from Bloemfontein to Johannesburg on the Airlink flight at 18:35. I however arrived much earlier at the Braam Fisher Airport on the 13th & requested the personnel at the Airlink counter whether there was an open seat on their flight that was going to depart at 11:00. I was advised that the flight was fully booked but I suggested that I will wait at the counter as someone might cancel at the last minute. The lady at the counter then later advised me that the last two passengers have checked in & that I should wait in the restaurant on the airport until later when my flight was due. As I left for the restaurant I was called back to the Airlink ticket counter to be advised that there was a seat available for me, but that it was going to cost me. I agreed to make an additional payment as waiting for seven hours until my flight seemed a bit long. I was shocked to learn that I had to pay an additional R2 600 on top of the price I had already paid for my booked flight to get onto the flight. I however was so desperate not to sit at the airport the whole day that I paid & got onto the flight to Jhb. I was shocked to see that there was another open seat on the aircraft when I boarded it. Is there an explanation as to why I had to pay this much as the two seats would have in any way been empty on the way to Jhb?