According to Lost Planet executive producer Kenji Ohguro, via Lost Planet 3 producer Andrew Szymanski's translation, the upcoming E.X. Troopers exists because the developers on Lost Planet 2 weren't able to successfully marry up the gritty story and the "festival atmosphere" created by the game's multiplayer.
"They had kind of struggled with Lost Planet 2 a bit, because they were going in this direction of creating this multiplayer, almost festival atmosphere, including crazy amounts of content and ridiculous scenarios. Sort of Monster Hunter with guns— coming in and defeating huge creatures together—and getting away from some of the narrative strengths that were originally part of the franchise," explained Szymanski, relaying Ohguro's words.
"They were doing this almost kind of ‘party game,’ but their art style was leaning more towards the cool end of the spectrum. So, he [Ohguro] already felt at the tail-end of Lost Planet 2, that they weren’t able to marry those as well as they should have. That was one of the reasons why maybe Lost Planet 2 didn’t perform as well as it could have. Coming out of Lost Planet 2 as the franchise owner on the creative side, Ohguro-san felt really strongly about the need to branch these out into two separate products."
The decision was then taken to separate the games into two: one would be a "party" shooter, with a visual style that reflected a more light hearted tone. The other would look to return to the franchise's roots that, according to Ohguro and Szymanski, present "more of a cinematic, narrative-driven experience that really touches upon the themes of colonization, survival, and that kind of stuff."
"The beginning of E.X. Troopers was, ‘Let’s take that party game atmosphere and make that its own product.’ And then, Lost Planet 3 is ‘Let’s take the core franchise values and make that into its own product,’” summarised Szymanski. [Siliconera]