Kessler syndrome was a specter for the space industries throughout the pre-Fall era. The amount of debris in orbit increased in step with the human presence in space, with orbital waste management taking larger and larger priority. Graveyard orbits became saturated, laser-brooms de-orbited loose, small objects, and specialized waste management vessels handled larger objects, but Earth's orbits were only barely being kept under the potential tipping points of a runaway cascade.
This careful management was thrown into chaos during the Fall, as inter-orbital war, first between the great powers, and then between transhumanity and the TITANs engulfed the skies. Broken and exploded ships, stations and space elevator pieces, and left behind orbital denial weapons systems and satellites surround Earth. Earth orbit is a storm of colliding debris (each collision spreading yet more debris), ranging from fragments massing less than a gram to derelict ships, most in orbits fast enough that even small specks can cause damage.
No agent, TITAN or transhuman, has established a deliberate deliberate blockade of Earth, but it remains thoroughly out of reach; the odds of landing on Earth are essentially zero, and even if you land, making it back to space is just as dangerous. Fear of TITAN attack and exsurgent infection remains high, and most habitats have rules forbidding the entrance of anyone or anything that has come directly from Earth.
Kessler syndrome can replace the deliberate interdiction through killsats in the setting.