Because that's the talent needed if he's looking for a Best Man.
"What?" I hear you ask? "Has she been at the gin (again)?"
Not guilty; just a bit of surfing - it's amazing what you discover when you spend half an hour with Mr Google. Last time it was Bridesmaids defending the Bride from erstwhile ex-lovers; this time it's whose sword arm is up to scratch.
Because that was the criteria for the Best Man. Depending upon the era (some of this goes back to Biblical times) and the culture, the Best Man's job was either to prevent the bride from escaping after she had been forcibly kidnapped from her family in order to marry the Groom (he must have been off school when they had lessons in charm and wooing - you shouldn't ever get married unless you've had a good woo), or to prevent a Bride's family trying to grab her back when she was escaping to marry the man she loved.
Whatever the scenario, this was a role that was taken very seriously. As well as being able to wield a sword, there were often weapons hidden under the floor of the church so the other Groomsmen could lend a hand if necessary. And when all was done and dusted, the Best Man spent the night guarding the bedroom door of the newly weds so 1) the Bride couldn't leg it before the consummation, and, therefore, get the marriage annulled, or 2) the Bride's family couldn't snatch her back before the aforesaid deed was done.
And today's Best Men have a meltdown over organising a Stag and looking after a pair of rings. Hmm, I think they need to get a grip.