In DNA fragments have sticky ends, one end of one segment has a sequence complementary to any of the ends of the other segments. Until and unless two ends are complementary they will not be able to bind to each other via a phosphodiester bond. Please note that 3’ end of one DNA fragment binds to 5’ end of second DNA fragment. The given diagram illustrates hanging, complementary ends:
On the other hand, DNA fragments which have non-sticky ends do not have single stranded complementary sequence to bind. The given diagram illustrates non-hanging ends. Note that there are no single stranded complementary ends to which the strands could bind. They are already complete.