Ideally, a kid coming out of high school is looking to get an education... The way college tuitions are these days, plus the difficulties in paying off school debts, it's an excellent opportunity afforded to hundreds of kids every year which they wouldn't otherwise have. The reality is, there are many in CFb who are dreaming more about making it in the NFL, and college football is the next step in getting there. If a talented kid is getting benched and he thinks he has the goods to make it at the next level, then he may feel compelled to switch schools where he has better opportunities to showcase his talent. Then there are others who are competitive and simply enjoy playing the game; John Dewberry wasn't getting any playing time at UGA and told Coach Curry if he started at Tech, he'd win ball games for him!
As far as coaches go, it's probably a reflection on where society is today. Look at how the work force has changed over the last couple generations... My dad was able to make a 30-year career with the same company. Although his industry was very competitive and he had to survive a couple waves of massive layoffs, many people from his era had the luxury of spending their career with one company. The way later generations viewed work changed drastically... Boomers wanted more upward mobility, and people in my age bracket wanted to balance work with family and quality of life. At the same time, the economy became more competitive and large firms began stressing the bottom line above everything else. Employee loyalty and company loyalty steadily evaporated.
Against this backdrop, you can begin to see how coaching changed as well. No more do we see the Bobby Dodds, Vince Dooleys, Bo Schembechlers, Bear Bryants, etc. who spent decades on the sidelines with a single team. No more do you see assistant coaches coaching 10 or 15 years at the same school, content to remain in the shadow of their head coach or wait their turn to take the helm. Changing schools became a way of upward-mobility. Also, in the competitive area of today's college football, where fans and alumni are increasingly impatient for success, high rankings, and divisional championships, coaches are on the hot seat much more than in years past. He may only get three seasons to get things in order, or else he's out. Loyalty between coaches and teams seems to be a thing of the past.
I grew up a fan of Georgia Tech during the Pepper Rodgers years; I'd dreamed of one day playing at Tech for Pepper for many years. He was fired the year before I entered high school, but the desire to don the gold helmet and play football at the Flats was still there and never really died. In the end, I was too small (underweight and small-boned) to play at that level, but if it were at all possible, I would have jumped at the chance to walk on and at least be on the practice squad.... hoping to get some playing time here and there. I don't know how much that mentality exists much anymore. But imagine wanting to play for a particular school and getting a free education on top of that... how could you bite the hand that gave you that opportunity by transferring? (As it's often been said, if a young player has the goods to make it in the pros, the NFL will very often find that person).