Why were lightships replaced by automatic buoys in the late 20th century?

In the late 20th century, lightships were replaced by automatic buoys primarily because they were costly to operate and maintain.1

As specialized vessels, lightships required significant resources, including regular overhauls every two or three years, making them prime candidates for automation. While lightships were historically valuable for marking shifting hazards and key traffic positions where permanent lighthouse construction was impractical, the development of more efficient, unattended navigational aids allowed for the transition to automatic buoys.12