Explaining では all at once is impossible, but I think you might be able to think this way.
As for in Thai, this dish is very popular.
You know the particle は is the topic maker, don't you? By putting は after で, namely, you can topicalize タイで to draw more listener's attention to タイ as a place where of 非常に人気があります.
タイではこの料理は非常に人気があります。 As for in Thai, this dish is very popular.
タイでこの料理は非常に人気があります。 This dish is very popular in Thai.
この映画を、一人で見るべきではありません。 You shouldn't watch this movie alone.
この映画を、一人では見るべきではありません。 As for alone, you shoudn't watch this movie.
You can draw more people's attention to the method of alone to wathc the movie than simply saying 一人で.
このカフェで、タバコを吸ってはいけません。 You can not smoke at this Cafe.
このカフェでは、タバコを吸ってはいけません。 As for at this Cafe, you can not smoke.
You can draw more people's attention to Cafe as a place where you can not smoke than simply saying カフェで.
At this point, you might wonder if you can put particle は two or three times or perhaps more on a sentence. The answer is actually YES.
Does my explanation make a sense for you??