According to [1], these particular ones exist because of legacy encodings of Serbo-Croatian,
Digraphs ⟨dž⟩, ⟨lj⟩ and ⟨nj⟩ in their upper case, title case and lower case forms have dedicated Unicode code points as shown in the table below, However, these are included chiefly for backwards compatibility with legacy encodings which kept a one-to-one correspondence with Cyrillic; modern texts use a sequence of characters.
According to [1], these particular ones exist because of legacy encodings of Serbo-Croatian,
[1] https://en.wikipedia.org/wiki/Gaj%27s_Latin_alphabet#Computi...