why cant java concatenate full strings code example

Example 1: String concatenation in java

// String concatenation in java using concat() method
public class StringConcatMethodDemo
{
   public static void main(String[] args)
   {
      String str1 = "Flower ";
      String str2 = "Brackets";
      String str3 = str1.concat(str2);
      System.out.println(str3);
   }
}

Example 2: java best way to concatenate strings

// StringBuilder
String stringBuilderConcat = new StringBuilder()
    .append(greeting)
    .append(" ")
    .append(person)
    .append("! Welcome to the ")
    .append(location)
    .append("!")
    .build();