As a teacher, I can assure you that this phenomenon is very real! All too many parents are overly involved. I do see the parents who are living through their children, especially with sports and clothing -- those parents tend to be the ones trying to live their lives through their teens. I do see parents who've "helped" their children with projects throughout elementary school, and the kids reach high school without really understanding how to set goals and work towards a finished project independently. Sadly, those parents seem to think they're doing something good, when in reality they're setting their kids up to need more help later.
How'd we get here? I think there are two big factors:
1. We've raised our expectations. That is, we've raised our expectations for everything: we expect to live in bigger houses, to go on nicer vacations, to drive nicer cars, to eat better food, to own better TVs and phones and other toys, etc. To look at just one example, consider appearance: It's no longer good enough to be dressed nicely; instead, ladies are expected to be thin, to have highlighted hair and professionally done eyebrows -- don't forget the tanning and nails. Clothes become outdated practically as soon as they're out of the bag. In about a hundred different ways, "average" is no longer good enough for us.
Of course, this translates over into parenting! It's not enough to raise a nice child with good manners who makes average grades. Instead, too many people feel the need to raise a perfect child with straight As, athletic ability, membership is a dozen clubs, and more! You don't get these results without pushing, and many people push too much!
2. We have fewer children and more conveniences around the house. My mom had five children, and a lack of money forced her to spend much of her time sewing, gardening, canning, and cooking from scratch. She literally didn't have time to micro-manage our lives, and it was good for us. We had to learn to stand on our own two feet.
In contrast, most of my friends today have only two childen, and though many work long hours, they have less to do at home. Many cook only occasionally, have yard services to do their lawns, etc. That leaves more hours to obsess about those two kids. Also, many of us today have more money than our parents did, and it's easy to spend-spend-spend on kids; though this isn't the same thing as hovering, it is closely related.
To argue the other side of the coin, it's absolutely true that there's "more" out there than when we were kids, and it's easier to make mistakes -- and many of those mistakes are really, really hard to escape. Kids absolutely need guidance, and parents have to walk a fine line. When does guidance become enabling? The line is probably different for each kid and each situation (for example, my 6th grader breezes through all her homework -- except for math, and there she needs lots of extra help). Every parent makes a mis-step now and then and gives too much or too little; the key is to find that right balance.