The dust is ejected from the comet at relatively low speeds and the particles therefore remain in orbits that are very similar to the comet’s. Lots of objects

The dust is ejected from the comet at relatively low speeds and the particles therefore remain in orbits that are very similar to the comet’s. Lots of objects in similar-but-different orbits quickly diverge such that they spread out along the entire orbital ellipse. So think about it more as a stream of objects in the shape of the comet’s ellipse. The whole area of the comet’s orbit is a “high traffic zone” for small particles, and where those streams cross the earth’s orbit you get meteor showers. Imagine two small pebbles ejected from a comet at the same time, one in the prograde direction (ie. in the comet’s direction, ahead of it) and one retrograde. For the first pebble, at the point 180 degrees opposite on its orbital ellipse, it’s orbit has been raised by (say) a few thousand km, while the second pebble’s orbit has been lowered by a few thousand km. If you zoom out you can barely tell the difference - on a solar system scale the ellipses look almost identical. But the difference in velocities means that they will quickly start to diverge in time. Both pebbles will do a full orbit and return roughly to the same point in space where they were ejected. But the retrograde particle (ie. the one “dumped out the back” of the comet instead of the one “fired ahead” of the it) will arrive there much earlier - it went faster and had less distance to cover. Repeat with millions or particles and you get a cloudy stream along the ellipse.