If you're looking for reasons why people may not have completed your game, it's important to understand the circumstances. In general, it's a game jam and people plan on playing a bunch of games, so unless the challenge your game poses is compelling enough to inspire the player, they may play it to get a taste, and even if they don't finish it, still give it a rating from their experience of it. I've played through your game, I also didn't complete it, and there was a couple gameplay things that got in the way of that. The collision on the different boxes wasn't exactly reflective of where the edge of the platform was, so I kept pressing jump and calling through the corner of the platform, which was frustrating. There was sometimes slight input delay, which also meant missing jumps. The screen scroll mechanic is good for a game like jump king if you intend the player to use trial and error to find the right path over an extended period of time, but you having built the levels already know the path. I spent a good while just trying to figure out how to get up onto the second screen, the jump to land on top of the first block at the bottom of the second screen was already quite the challenge to figure out, and once I knew, the execution wasn't that easy. I don't think your game is flawed necessarily in these aspects, it's simply reflective of the games you took as inspiration. But for the bounds of the challenge, trying to create a speedrunnable game, while the end result might be speedrunnable, if you make the process of learning it tedious and difficult, people aren't going to stick around long enough to learn the speedrun. If you're looking for some tips to improve, I'd recommend the following:

• Increasing the size of the collision boxes for the platforms, they should be forgiving and let the player use the whole extent of the asset
• Introduce coyote time, a brief 0.1 sec window or less where the player can still jump once they've left the platform
• Easing into the challenge a bit more, having the first challenge only consist of disappearing blocks makes the first screen too punishing to be learning the controls
• Have some visual indicators of the intended path for the player, that way even a player who's stuck can figure it out

Hope this helped, and please don't take any of it personally, the game you made is really good on its own, it just lacks some of the minor details that adhere to the specifics of this game jam theme.