The no show fee was originally applied to only the most popular restaurants. It's in place as a deterrent. They later realized it was a good $ maker for all restaurants, but the starting motivation was to try and cure the no show problems with their most popular spots. They were getting flooded with complaints, so they tweaked the system to make it more difficult to double book and to punish those who decided to ditch on their ADRs. Restaurants can't run efficiently if people who make reservations fail to show up. Plus, if you've ever seen some of these walk up lines ... it can get pretty nasty.
I don't always love the policy since I like some flexibility, but also know there's very little of that with popular spots. Still, I try and think about the other people who are dying for these ADRs. I've given up a BOG ADR before. I held it for a bit because I wasn't 100% and I knew I'd never get it back, but in the end (well, really 3 mos out) I knew we'd likely not make it and it would be nicer to give it to someone who really needed it.