I think it largely depends on the individual's situation. I know some families with 3 or 4 kids all going different directions after school and everyone (including mom and her taxi) doesn't get home until 6 or 6:30 at night. Unless you are accustomed to eating dinner at 8 PM, that doesn't leave a lot of time to start making dinner unless some prep work has already happened (not to mention there is still homework to supervise, notes to read and sign, etc...).
Not everone can afford to feed their families steaks and boneless chicken breast. Some families also make a lot of work for themselves be catering to picky eaters and making their kitchens short-order diners (a different thing for everyone because Son A despises green beans and Daughter B won't touch red meat or onions and DH 'feels like' chicken tonight even though you had hamburger thawed out.
).
Not everyone is organized and/or plans ahead.
Also (and this is just my opinion, folks), parents who don't get their pre-teens and teens involved in making the evening meal have nobody to blame but themselves for being short on time. When I was growing up, my best friend and her brother were each responsible for planning and making one dinner each and every week by the time they were in 8th grade and I fully intend to implement that plan with my daughters in a few years as well. I enjoy cooking, but I have been the chief cook and bottle washer for this family for over 20 years now and it's high time I started getting a break every so often.
That said, I cook meats ahead, make double portions of casserole type dishes and soups (freeze one for later when you've had a crazy day and the last thing you want to do is have to make an entire meal when you get home), pre-cut veggies and use my crock pot a lot. But you know what? Even I'm guilty of having the kids pull out a frozen pizza and make their own dinner every once in a while and I just reheat some leftovers for myself. If they're going to be expected to make a complete meal in a few years, now's the time to get them used to using the stove and oven.
Somebody could probably make a killing teaching busy moms and dads how to plan ahead and cook quick meals without having to stress about it every night.