[amluto]

It’s because the “re-emission” is coherent in the sense that it’s in the same phase as the incoming light. As a decent analogy: when you sing a pure note, it “excites” (vibrates) air molecules as it travels, and those air molecules in turn bump into other molecules, all at random, but still all in phase so that whoever is listening hears the original note. Similarly, when light goes through ordinary glass, it wiggles the electrons in the glass, which in turn change the way the light propagates, refracting it while still preserving an image.

Any textbook on electricity and magnetism will cover this in a section called something like “Maxwell’s equations in materials”.