I made the following analogy in a BIONICLE-related Facebook group I'm in, and my twin brother Lyichir says I should post it here as well, so here goes.
Think of BIONICLE as horse racing. LEGO is betting on a horse race for the first time in five years. If they win, they will have enough money to bet on future races (future waves of the theme). If they lose, they give up on betting on horse races forever, because it's no longer worth their time and money. There are many, many horses (potential customers) in the current race that are young, fit, fast, and enthusiastic, just like past winners have usually been.
Then there are a small number of older horses that were regular winners years ago, but they were already getting old the last time LEGO bet on a race, and haven't raced at all in five years. They are by now becoming too old for racing, they run slowly (in this analogy, don't tend to buy sets as regularly), and they have every intention of jumping the track the minute they get the sense that they don't like how the race is turning out.
Which horses do you think LEGO should put their money on? Remember that this is their only chance to get this right. If they lose, they quit betting on horse racing (in other words, give up on BIONICLE) entirely. As Greg said on the LEGO Message Boards, this is something that LEGO only really has one shot to get right.