[fernando]

I wouldn't know about the fashion issue, but it was a vital advantage to have a longer reach than your adversary in a duel. There were indeed royal laws limiting the length of swords. King Dom João III, for one, allowed a maximum five and half palms ( some 120 cms.). Longer specimens were then called 'off mark', some of them reaching the seven palms.
Noteworthy the limit prescribed comprehended the whole sword; you could have a normal blade and a longer hilt, which would give the same effect.
One alternative to evade the law was to commission 'extendable' swords; you would go around with a legal weapon and only stretched it for a duel.
As then Monarchs considered themselves above the law, there is no surprise that, in the arms inventory of King Dom Pedro II, inherited from his father Dom João IV, it was listed an item called "sword that grows".

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