If you watch the PGA tour, you'll notice caddies are carrying cart bags. Naturally, you're probably wondering why they don't opt for a standing carrier since they're easier to lug around. There are a few reasons why pro caddies do this, such as:
Sponsorships. Since they are large, it's far easier to place a brand's logo on them.
Access To Clubs. The golf club dividers tend to be well-made. So pros can access their golf clubs without them getting stuck or the grips rubbing against the bottom.
More Storage. As you can probably guess, the pros tend to bring many items onto the course with them. Whether it's a towel, water bottle, golf balls, or snacks, they offer plenty of storage space.