They could've, yes. But with each translation of the original japanese script, you lose some fidelity to the original way it was written and meant to be told.Good work!
What I mean is, if you had trouble translating from the japanese, you could have taken that translation and translate it to english. Am I right?
If the Spanish team lost 5-10% (of fidelity) in translation, and the team would've translated the spanish script and thus lose another 5-10% in fidelity, their text would now be very different from the original one.
So translating the original text with people that can speak Japanese takes roughly the same amount of time and remains very close to the original work. I'm actually glad this is the way they chose to do it, even if it took 4 years to do.