In English and Spanish (and likely other languages), the past subjunctive is used with conditional clauses:
It would be better if we went to the beach.
Sería mejor si fuéramos a la playa.
Here, the bolded verbs are in the past tense and subjunctive mood (although the latter is indistinguishable from the indicative in the English example).
Why is this the case? It would seem more logical that present tense were used because these statements are frequently generalizations or present truths ("should we X?" "it would be better if we ..."), for which the languages in question use present tense.
I'm just curious as to how this usage developed and why the past tense came into use here.