I run an agency and there is a strategy behind this. Some of our clients are focused on getting a larger number of followers quickly. To do this we set our targeting to be very open and in the cheapest markets. You’ll get a lot of fake accounts and teens in 3rd world countries that aren’t your target audience. But if you want big numbers fast and cheap this is how you do it. It does make your account look more credible when you have tens of thousands of followers.
We have other clients that are more concerned with getting followers in their customer demographic, especially in certain locations. These tend to be significantly more expensive.
If we’re launching a new brand sometimes we’ll run open open targeting for a few months to push up the follower count, then switch to a more targeted following.
These are all legit tactics, you just have to figure out what’s in line with your goals.