Ok so a few things to note here that are already suspicious
1. This plane is going way too fast at the end of the runway even for a belly landing. It's practically doing V1 speed here. The runway is 1.8 miles!
2. Spoilers are not engaged (but reverse thrusters are). This makes no sense
3. They didn't even circle to try and solve the issue. That also makes no sense, if your landing gear isn't deploying, you take a few minutes and figure it out??
All this points to catastrophic, but unlikely malicious pilot error. I bet they forgot to lower the landing gear (maybe distracted by a birdstrike?), then landed on the belly, couldn't figure out what was going on so tried to abort the landing and accelerate, only to not be able to rotate (even this doesn't explain reverse thrusters)
BREAKING: Video shows crash of Jeju Air Flight 2216 in South Korea. 181 people on board