The airport company isn't just about passengers to the sun. If it collapses what happens to BAMC? Global Trek? Caerdav? E cube? All the businesses that rely on it like hotels, pubs, car parks etc.
Also the airport sector in England has had £100 million of support, Scotland £34 million from the Scottish government and EU if I've read it correctly and N. Irish airports £10 million from the Northern Ireland government. The Welsh government obviously value the airport business to secure its future in such a big way.