It may seem uglier if you use it first time:
#+BEGIN_SRC lisp
(format t "Hello world!~&")
#+END_SRC
but it has two things going for it.
One, it's consistent with other blocks, like BEGIN_QUOTE, BEGIN_EXAMPLE, BEGIN_VERSE, etc. (n.b. all four have a default shorthand that gets tab-expanded; <s. <q, <e and <v, respectively) , and with arbitrary user-defined blocks like BEGIN_whatever.
Two, while #+BEGIN_SRC may seem only an unnecessarily verbose way of writing ```, things change when the block starts to look like this:
#+NAME: advanced-block
#+BEGIN_SRC lisp :package my-package :var foo=123 :var bar=asdf :noweb yes :exports both :eval never-export
<<preamble>>
(format t "Hello ~A!~&" <<some-other-block(param=3.14)>> )
#+END_SRC
AKA. a named source block (so I can reference it elsewhere) of Lisp executing in selected Lisp package, with org mode variables injected into it, using noweb syntax (literate programming) for injecting other code blocks[0], which when exporting the document to a different format (say, PDF) will export both code and results of its evaluation, but will not automatically evaluate the code.
This feature makes Org Mode essentially a kind of better Jupyter, with automatic support for any and all possible language that you can plug into Emacs, simultaneously.
--
[0] -- here, it'll paste the literal contents of #+BEGIN_SRC block with #+NAME: preamble at the beginning, and then paste the results of executing a block with #+NAME: some-other-block, with value 3.14 for its :var param, at the end