This is just a theory

From what ive heard

It has something to do with the thin bezel of modern phones design

The display cable have to to flex 90° and bcus of the thin bezel they are not enuf room casing great strees and hence the connection break over time due to thermal degradation and orher enviroment stress.

Dats why on older phone with thick bezel like my samseng note 3 no such green line prob even after 11years.