This is not a new phenomena. When my daughter turned sixteen she got her license immediately, yet many of her friend who turned 16, 17, 18 and did not get theirs. It has just kept growing from there.
As to why. The trend that began with millennials has been amplified by Generation Z, with teens citing a myriad of reasons for putting off or avoiding getting a driver license. Some prefer more environmentally friendly transportation options, some found driving too stressful and some just don't care about cars.