How was malaria actually eliminated in some countries?

One reads about the fight against malaria that it was actually
eliminated or almost eliminated in some countries such as the US, southern Europe, much of China, Cuba, etc. etc. with a combination of changing wetlands and use of insecticides. But how was it possible to eliminate EVERY malaria carrying mosquito, every one in these areas? I certainly still see swarms
every summer and I read that the anopheles' range still covers
much of southern Europe and the USA up to Rhode Island. So how was malaria actually exterminated there? And if it was so easy (comparatively) why wasn't it similarly done in more countries, or at least in more countries with wealth and health infrastructure equal to what it was in North and Caribbean America and southern Europe when it was eliminated there?

DDT, lots nad lots of DDT. Malaria has resurged where the negative efeects ( and they are nasty) have convinced public health officials to reduce or eliminate spray programs