Banking Evolution

It's amazing how banking has evolved these days. Gone are the days you need to open a "bank account" to "store" your money in the bank. Now, you can just "buy" a cash card and enjoy the safety banks offer in "storing" your hard earned money without the unnecessary (just an opinion) "maintaining balance" requirement. Until now, I don't quite get the idea of banks charging a fee if your account falls below the "maintaining balance." Hey, that's my money!