Punter57, when those bookies were "behind" because of all those favs. winning *they were really NOT behind at all*, that's worth repeating a hundred times * they were really NOT behind at all*. The reason why is because of the laws of mathematics regarding the situation.
A bookie knows, because of the applied maths, that those *seemingly* successful bets WILL NOT continue to be successful, and there's a 100% guarantee on that. Those punters would have falsely thought they beat the bookies with those bets on the winning favs. The next week they would have re-invested some of those winnings , then the week after, then the week after etc etc etc. All the money the bookie seemingly lost on his so called bad day, he will re-coup, he MUST..... because the odds and percentages are in his favour. It's completely irrelevent whether those punters re-invest those winnings over 1 week or 10 years..... the exact same laws of mathematics and averages apply. The ONLY way those punters who won on that day can keep their profits is to NEVER bet again on the horses... they must lose long term, because the odds and percentages are NOT in their favour.
This is also the reason why people believe they have winning methods or systems...... they check both past and present results and they think it wins; after all the results are there to see. They then start operating it in the real world and sure enough, after the first few months, or even years, they are in front; whoopie! A "winning system" they believe.
Little do they know that at some point they will begin to lose, they'll still be confident though and expect to re-coup the inevitable losses. Eventually the system will fall behind and the poor punter will be dumfounded, completely mystified as to what's happened. Well, I'll tell you what's happened....... the bookies have gladly accepted this punter's bets fully safe in the knowledge that the percentages are on the bookies side and they know that eventually the bookies must win.
That's the reality of the cruel world.

At the end of your post you mention the punters getting the better of the bookies on a fav. bet and being better informed than the bookies (at least regarding this one fav.): And you ask why this can't happen more often. Well, I'm afraid those punters were definitely NOT better informed, just as the bookies are not better informed when the bookies win. Because of the very, very, simple law of averages the punters MUST back favourites that win races .. that's obvious. When a Fav. romps in the punter *thinks* he beat the bookies with logic and insight....... the law of averages dictates that a certain number of favs. MUST win...... they MUST win regardless of whether the punter has greater or lesser knowledge than the bookies.
And like I sad, the punters will eventually re-invest the money they *think* they won.... they will eventually end up back at square one and wonder how it happened.
It's all about percentages... it's not about picking winners.
The only chance for probably 99.9% of punters to win is this.......... firstly make sure you are not behind with your punting to date (this refers to your entire history of betting over your entire life to date..... this of course disqualifies nearly everyone), now start betting using any method whatsoever you desire; set a profit goal and as soon as you reach that goal....... quit betting for life. For close to all of us, there's no other way to make a *permanent and genuine* profit on the punt.