[Vespers War]

I could see Spain being extremely wary about deploying forces to the east if the situations with ETA and Morocco both went bad at the same time. Deploying an expeditionary force to help Morocco would be a priority for both Spain in particular and NATO in general to make sure the Straits of Gibraltar remain friendly on both coasts.

Tweaking the outcome of Black October in Algeria so that it gains support from the USSR rather than Bendjedid dismantling the socialist system (and even removing the word "socialism" from the constitution entirely) puts Morocco under more of a threat, given Algeria's pledge to support Western Sahara. A combined Polisario uprising and Algerian invasion would demand a Spanish intervention that would be even more of a priority than sending forces east.

Similarly, if Euskadi Ta Askatasuna had things go slightly differently, it could have repercussions on Spanish deployments. In 1995, they very nearly assassinated Jose Aznar, the Conservative politician who became Prime Minister the next year, and there was an attempt on Juan Carlos I on Majorca in 1996. Either or both of those attempts succeeding would force a much stronger reaction than Spain actually had, likely involving military action in the Basque region.

Between the two of these, enough forces could be tied up that Spain has little or nothing left to send to an eastern front. Spain's populace wasn't nearly as enthusiastic about NATO as its leadership (only 52.6% supported remaining in NATO in the 1986 referendum), and Spain's military wasn't integrated into NATO until 1999 in the real timeline; that might have been accelerated slightly in T2K timeline, but it would need to be massively accelerated to significantly affect the Twilight War. If someone felt so inclined, the government's decision to send Spanish troops to fight a "foreign" war while significant problems were on Spain's doorstep might even be the catalyst for a second civil war.