Why did Americans fall in love with Chinese food?

Because it was inexpensive and convenient.

Mainstream American consumers disliked, even despised, Chinese food for half a century after its arrival in the United States. Around the turn of the twentieth century, when Americans began to frequent Chinese restaurants, they largely stayed away from the exquisite foods, such as sharks fins and birds nest, that many Chinese and non-Chinese food connoisseurs regarded as representing the essence of Chinese cuisine. Instead, American restaurant-goers preferred such simple and inexpensive dishes as chop suey and chow mein. In other words, Chinese food rose in popularity not because of its gastronomic merits but because it met the swelling demand of the growing urban population for a better and more convenient lifestyle.