Spain did fulfil obligations towards Germany and Italy after the war to repay the debts incurred for all the aid. This was mostly in the form of mining concessions in the north, many of which were given full German ownership. Those mines provided important iron ore and tungsten to Nazi Germany right up until 1944 when the land link between the countries was cut by Allied forces advancing in France.

There was also an opportunity to join the war as a combatant, which I assume is what you consider obligations to Hitler. Franco and Hitler held talks at Hendaye in southern France in October 1940. In these talks, Franco demanded significant concessions including Gibraltar and a substantial chunk of French northern Africa. Some suggest that this was intentional and that Franco never intended joining the war properly, or wanted to delay his entry long enough to know that he'd be on the winning side. The talks inevitably failed, and Spain never entered the war (as we can all tell), but as others have mentioned some volunteers of the Blue Division did serve on the eastern front.

Additionally, there is the consideration that the defeat of a left wing government on France's flank was of enough strategic benefit to Germany's interests for Hitler not to demand too much more out of Spain, so long as they weren't part of the western allies. Spain's strategic position also allowed German and Italian access to Spanish Atlantic and Mediterranean ports as well.

As a whole, the Spanish military and economy were in ruins too. Exhausted after 3 years of war that took the lives of hundreds of thousands and imprisoned many more, destroyed much of the economic infrastructure, and left everyone desiring anything but more. Spain's entry into the war would have essentially been a major weakness in the axis defence; the Spanish army at this point would be unable to defend adequately against any allied incursion. This would require additional German and Italian troops and resources to be sent to Spain just to secure the fact that it won't fall easily (which Franco had also requested as a condition for entry at Hendaye), which is really not worth the return of an exhausted and weak army as an ally.

Sources:

Viñas, Angel & Seidel, Carlos Collado. Franco's Request to the Third Reich for Military Assistance

Preston, Paul. Franco and Hitler: the myths of Hendaye 1940

Follow up question related to this;

Had Spain actually entered the war as a combatant, what would that have done to the region? Would Portugal then be forced into the war?

As I supplementary reply, I think it is important to note the role that the German Abwehr commander, Wilhelm Canaris played in Spain's "neutrality".

Quote from the relevant wikipedia article detailing the life and doings of Wilhelm Canaris:

Partly as a result of this fear of Hitler's plans, Canaris advised Franco not to permit German passage through Spain for the purpose of capturing Gibraltar.[49] Arguments used by Franco to counter Hitler's demands for German access to Spanish territory were influenced directly by Canaris, who met with a number of Franco's top advisors. Franco's position at Hendaye was greatly influenced by Canaris.[50] Additionally, a significant sum of money ($10 million) was deposited by the British at Churchill's urging in Swiss accounts for Franco and his generals to maintain their neutrality.

Also from the same article:

In December 1940, Hitler again sent Canaris to Spain to conclude an agreement (through strong coercion if necessary) with Franco for Spanish support in the war against the Allies, but instead of prompting the Spaniard to acquiesce to Hitler's desire, Canaris reported that Franco would not commit Spanish forces until Great Britain was defeated.[85] Conversations from this period between Franco and Admiral Canaris remain a mystery since none were recorded, but the Spanish government later expressed gratitude to the widow of Canaris at the conclusion of the Second World War by paying her a pension.[86]

I am sure that after Franco's obstinence in early talks with Hitler of entering the War, the Axis leaders decided Iberia would be better off for their purposes as a neutral region.

Remember that initially, Hitler wished the same for the Balkans.