Why didn't Francoist Spain join NATO?

One thing, that, I've never fully understood is why Francoist Spain didn't join NATO, like Salazarist Portugal did, the two regimes were pretty similar. Was there ever an opportunity for it?
 
Maybe leaders of NATO countries with good eyesight and sharp memory would have noticed and remembered Salazar failing to appear in certain photos taken in Hendaye on January 23rd 1941 (because he was not there).

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Salazar's regime was mildly authoritarian and friendly towards the Allies in World War II while Franco attained power with backing of the fascist states and engaged in a policy of pro-Axis "non-belligerence".
 
A Soviet Union that pushes Communism "to the Rhine" will probably result in Spain getting an offer to join NATO, which in this scenario they'd probably accept. As for why it didn't happen OTL, basically Washington wasn't fond of Franco, and vice versa. Spain did get aid from the US eventually, but not on the same level that other countries got Marshall Plan aid. One thing to remember also is the colonial issue. Spain had a few, but that didn't help matters. Washington made a point of pushing countries even in NATO, like Portugal, to drop its colonies.
 
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