I'd like to read answers to this from my American readers or foreigners who have lived in the US and observed things first hand.
The United States is a very large country with 50 states and a population of 330 million. It's the third largest country in the world by area covering about 9.5 million square kilometers and ranging from the Arctic north coast of Alaska to the entirely tropical state of Hawaii.
Many of us who are not American have heard about different local cultures in different states. For example, Louisiana used to be owned by France and I've heard the local people may still use a few French loanwords here and there. The cuisine has an element of French and creole cuisines. The northern Midwest attracted a lot of Scandinavians, Finns, Germans and other northern Europeans from what I've heard. There are towns where one of those ethnic groups is still dominant in the northern Midwestern states.
Florida is in the south and I can imagine it is or used to be clearly in the southern cultural zone. But its population has boomed in recent decades. In 1960, the population of Florida was only five million. Last year, it was 21.5 million. That's huge growth. From what I've heard, a lot of northerners have moved into the state attracted by the warm tropical climate particularly in the south. Other southern states have seen fast growth as well, facilitated by programs to eradicate malaria as well as air conditioning becoming common in homes and public buildings. If you have lived all your life in Florida or some other southern state that has seen large scale immigration from other parts of the country or from foreign countries and are old enough to remember how things were many decades ago, would you say that the character of your home state has changed from your youth? Is your home state now populated by large numbers of people who do not speak the dialect you learned as a child?
Would you say that different parts of the country have become more similar or more different in recent decades? I would guess more similar because of more migration across state borders and more immigration from abroad, more road and airline traffic and the proliferation of broadband internet connections and the same brands and the same shows being watched on Netflix etc. everywhere. But you can't know that without having first hand experience.