Why do soup with croutons require a breach on the soup and the croutons. Aren”t the soup and croutons something that is mixed together and is eaten in the same spoonful.
According to the general guidelines you are correct, we should seemingly need to decide on one bracha for this mixture. The Magen Avraham explains that this case is an exception. On the one hand we have a rule that in a mixture the Mezonos is always considered the main component [ikar] and the bracha is made on them. On the other hand with a soup it is impossible to say the croutons are the main component. So the soup remains the ikar, but because of it’s special status, mezonos croutons can’t become the tafel [secondary ingredient]. Hence, two brachos are required.
Mishna Brura 205:11, Magen Avraham 205:6