Remember in AD&D the attack round was 1 minute long and characters made multiple attacks in that time but only one that really matter, which you rolled on.
As an aside, there's no real reason a 6-second combat round can't be viewed the same way. Cinematic swordfights pack a huge number of blows into six seconds. There's every reason to believe that in a typical combat round the participants are mixing it up pretty good, and the attack check represents being able to actually gain advantage from the exchange.