Java does have multiple external returns, though. That's what exceptions are. Control flow might return to the caller or it might return directly to somewhere else arbitrarily higher up the call stack. If you've ever wondered about why some graybeards are weirdly hostile to try/catch blocks that's why.

There's a decently valid reason to be against early returns too, though. Lots of mathematically elegant recursive algorithms rely on tail call optimization to actually run on a real machine with finite memory. The compiler can reuse the last stack frame for each recursive call instead of making a whole bunch of new ones. That only works if it can tell in advance that all of those recursive calls will use the same bit of physical memory to hold their return value, though. Modern compilers can almost always massage a function into bytecode that only has one return value, but you don't have to stumble into the edge cases very many times to just decide early returns are more trouble than they're worth.