Because it's co-developed by Dimps. Dimps sucks and has a tendency to ruin a lot of games because of their inept programming and tendency to forget what the original IP is like so they end up churning out the most mediocre thing they can because they're Dimps and they're helpless unless the person they're co-developing with are capable people.
...I don't like Dimps.
In all seriousness, the game was incredibly blase. The real draw of the game was supposed to be its 3D version of the 3L-LMBS (Rebirth's battle system) but Dimps couldn't even get that right.
The game's too easy. The game's essentially structured as a "let's go from this village to that village to that village for these cutscenes" sort of affair (because the game does rely on cutscenes a lot), the dungeons are barely worth mentioning, the game is like 15 hours long (and the only reason why it's that long is because there is no sense of quicker travel in the game so you're busy trudging back and forth ever so slowly), there's little puzzles in this game (which is something I'd liked about Tales games when I played Tempest), everything about the game just feels so unengaging from the script to the battles to the villages to the characters to how it looks to the sidequests even. The day/night cycle just doesn't even seem to matter at times. The world that the devs attempted to craft in Tempest is lifeless, and that isn't helped by the predictable script or the bland characters.
For a game that seems to focus so much on battles because of the encounter rate, it's incredibly obnoxious that the game is so easy. Even newcomers to Tales would find the game easy. The regular bosses themselves feel like regular enemies because there isn't much to their battles. The final boss is a complete joke. Dimps completely missed the point with the battle system in the first place. Instead of making the 3L-LMBS in 3D in the 3-on-3 battle system something to completely take advantage of and switch lines in 3D for strategic advantages, you're busy getting rid of enemies so quickly to even think of doing that. It's poor balancing and poorly-thought-out. You're essentially supposed to use the lines to back-attack the enemies. Either use the stylus to mindlessly regularly attack the enemy and easily win, or switch between the stylus and buttons to combo and easily win. I'm left-handed, so switching between the stylus and buttons isn't as cumbersome as it would be for a righty, but even then, it's kind of bonkers that it wasn't just limited to button input. Not to mention that the battle options feel so gimped compared to Innocence and Hearts.
The story's incredibly predictable (ie: it's all about racism, and every twist and turn is incredibly predictable because there is little to no effort to hide anything (ie: plot revelations, Arria, etc)) and it has that tendency that Rebirth did to beat the racism topic into the ground. The cast is very weak and lack development. Everything about the narrative and cast is so uninteresting, and the game doesn't do much to try to draw you in to appreciate them in any way. They're just there, and when they do something, you already knew they were going to do it because the game and its script lacks subtlety more than the average Tales game.
Essentially, Tempest's problem is that it's dull, it's essentially Cutscenes: The Game Mixed with Battles That Are Mindnumbingly Easy for most of your playthrough, and manages to be much lesser than the game it's trying to follow from (Rebirth). Even if Rebirth's narrative is downright crap and among the worst narratives in the genre, the character interactions and battle system redeem it.
