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How did the Oort cloud get its population of icy objects?

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Illustration showing the eight planets of the solar system in order from the Sun-Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune-depicted to scale by size, with labeled diameters in miles and kilometers. The Sun is partially visible on the left for comparison. — Solar system The planets (in comparative size) in order of distance from the Sun.

The Oort cloud is believed to have been populated by icy planetesimals that originally formed in the outer regions of the protoplanetary disk closer to the giant planets.1

As the giant planets in our solar system formed, their gravity gravitationally scattered these billions of icy bodies far away from their original vicinity. Specifically, Neptune, with assistance from the other giant planets, played a key role in ejecting these objects into the distant, roughly spherical reservoir that now surrounds the Sun.123

Because the solar nebula was too thin at such extreme distances (tens of thousands of astronomical units) to allow for the formation of large bodies, these objects could not have originated in the cloud itself; they had to be transported there from the inner reaches of the outer solar system.13