[Brian Pfleuger]

In short, things are popular because they have some combination of:

1)They're heavily promoted.

2)They're "cool".

3)They work exceptionally well.

.308 has the first two in spades, as far as folks are interested in using what the military uses. It's self-promoting and automatically "cool" and then popularized further by the folks who choose to use it because THEY think it's cool and folks think THEY'RE cool... etc, etc. Number 3, it probably has too, depending on your requirements, perspective and ability.

However, "popular" doesn't automatically include #3. In fact, a lot of times there are things that are actually pretty poor in function but #1 and #2 over whelm #3. As a particular example, consider the most popular trends in the archery industry. Virtually every one of them is detrimental to accuracy but they're all far more popular and "cool" than the best accuracy stuff.