What were the creator's motivation?

Because the pritimive data types dont have methods, and since strings are so common throughout programming they decided to do it like that. I think google is a better ressource to answer this question. That being said:

There are two different types of strings, string litterals and string obeject. A string litteral is what your wrote in your example, whats interesting about string litterals is that Java is smart enough to know that if two string litterals decleared in a program share the same content, they are stored in the same memory location and can therefor be accesed via the same pointer. (They are both stored in whats called the common pool, as apposed to heap)

String objects instead is delcared like any other object using the 'new' keyword. Now the difference between the .equals method and the == operator is that .equals looks at the content of the string where as == operator actually looks at wether the two variables share the same memory pointer. Example:

String myStringLiteral1 = "Hello";
String myStringLiteral2 = "Hello";
String myStringObject1 = new String("Hello");
String myStringObject2 = new String("Hello");

myStringLiteral1.equals(myStringLiteral2); // True, they have the same content.
myStringLiteral2.equals(myStringObject1); // True, they have the same content.
myStringLiteral2 == myStringLiteral1; // True, they share storage in common pool.
myStringLiteral1 == myStringObject1; // False, they dont have the same pointer.
myStringObject1 == myStringObject2; // False, they dont have the same pointer.

This also explains why string in java are immutable, seeing as two different string literals with same content share same common pool, modifying one will mess with the value of the other one. Which is why methods like .toUpperCase() dont actually modify the string but instead returns a copy of the string.

This is far from the full explanation, but i hope it helps to see why java creators decided to do it this way, it surely also has disadvantages perhaps relating to performance, but its not something you should worry about.

Hope this helped!