Perfectly possible to go for a long long time without hitting that run but it will happen, the longest run of winning favourites is 28 in a row so you can imagine the odds of a run of second favourites just placing at some point are pretty good.
The liability may be low but at a run of even 10 winners you're well into the thousands to stake just to win your tenner, try getting 6000 matched at the odds you want on a shitty Tuesday at ffos las and that tenner isn't looking so good.