Why hasn't there been a resurgence of seaplanes/flying boats as passenger on international passenger flights?

Granted they are limited to landing on coastal cities, but I can still see the use of these for transcontinental flights, and the fact that they do not require a complex infrastructure for landing on water makes them very cost effective. I am aware island nations still rely on them quite a lot, but I see few downsides for other nations not to keep using them.