Spantax were a growing and huge operation in the early seventies... but the downward slope already began around 1975. Fuel prices rose and the economy slipped from 1973, which made the Cv-990s and DC-8s more expensive to operate. But that wasn't the biggest problem; their purchase costs were low.
A second factor was the 'Tower Air' factor; even before the DC-10 crash in 1982, they had about 5 fatal crashes and a lot of other mishaps (as mentioned landing on the wrong airport, but the incident with 10 people dying because of poisoned food on board also hit the papers), so many travel agencies became hesitant to book them.
A third factor was that Captain Rodolfo Bay was friends with dictator Franco. After Franco died, he probably lost part of his credit, because Franco's government could and would organize landingrights and benefits for Spantax, while the new democratic government more tolerated than supported Bay and Spantax.
Spantax was in deep shit already when their DC-10 crashed in 1982. All the earlier crashes which were often blamed on pilot misjudgement (like the Cv-990 in Tenerife 1972, killing 155) were relived again, and many western european agencies cancelled their contracts. Soon afterwards, in 1984, Rodolfo Bay resigned to make way to reorganize the airline, but in the 80s Spantax kept loosing money, and ceased in April 1988.
nobody has ever died from hard work, but why take the risk?