Because Mr. Fatass and Tiny Crybaby didn't do so well from Frontier? I have noticed the numbers reducing from the start of 02. In 01, you have your standard bunch. They only added on top of it in 02. Then came Frontier (around 4 kids, but how it was handled with the gags is bleh), followed by Savers (By around that time, there were three), now Cross Wars.
Are they trying to save moneh by reducing to three kids? We have two teen anti-heroes with the usual crazy hair looming in the background, only to serve as watchdogs for.. someone. Plus those looming antagonists watching over MadLeomon.
By far once the teens join the heroes, it will be the standard 5 heroes again. :X
Confession: I've only liked the first season, and didn't really pay any serious attention to any other Digimon series since then. Honestly, the ideas I've seen so far that they introduced in each series pretty much dilute what the series was all about. First, it's fusing Digimon, then, it's reducing the group to three to four people. Then, it's people TURN into the Digimon, throwing the whole "friendship" thing from the series out the window. Now, aparently, it's "add a ton of Gurren Lagann influences about cocky dudes who do a ton of evolutions/fusions from the start, and make the digivices into Apple branded shaving machines.
Brooding teens with long hair and emo looks watching from nearby cliffs = dudes who will undoubtly be rivals/anti-heroes with own purposes/fight fodder who will join the heroes at certain points than retreat because it messes up their style to be part of the main group.
Seriously, anime gets so predictable in its narrative and clichés, they're pretty much doing a block puzzle by now. I got fond memories of the first Digimon show. Unlike the Pokémon anime, which I couldn't stand by that time, it was about kids who were actually in danger, who formed friendships with beasts so they could survive, and who travelled an epic world with charm and adventurish ways. By the end, they face the Apocalypse and win. End of everything. Nothing else required.