It is hard to pick a good scale for miniatures, since there are so many variables to consider. So, why 6mm and 1:1200?
Of course for example 15mm (not to mention 28mm) figures would give much more details and surface to paint, but I have very seldom seen an army in 15mm where army actually looks like army – usually there are far too few figures to make stands look like mass of troops (there are exceptions, but it usually comes with cost in game surface – and in extreme cases, storage). Therefore I tend to think that 6mm is about optimal for my purposes.
When saying that 6mm (or 1:1200 for age of sail) is optimal scale for wargaming, it is not only because they are easy to paint in large masses (very easy compared to 28mm for example), that they look more like an army when massed together, and they have quite lot of details for their size – unlike 2mm, which is another scale that looks pretty good in larger quantities. 6mm is optimal also because even larger battles can be set in normal household without need to dedicate entire room for the purpose. In fact, some decent games can be played in area of 2ft square.
In Age of Sail naval games, ships do require a bit more space to maneuver around, and range for the guns could become overwhelming in anything larger than 1:1200 scale.
Yes, I do agree that individual troopers may not exhibit the visual appeal of well painted 15mm or larger, but on the other hand, distance that the units are normally viewed give some relief for otherwise slack paint job. That said, there are exceptions proving that one can pull out same levels of detailing in 6mm than in most can out of 15mm (especially Alder 6mm – which as I have understood are somewhat larger than Baccus). I am not one of them, but can certainly appreciate the effort.
Lastly, opponents willingness and ability to field armies in same scale and in about same time is not least of the problems. Hence, I thought that by reducing the scale to speed up the painting, I could field few armies in same scale and then make games portable and more accessible.