According to Pirkei D'Rabbi Eliezer (Ch. 16), a groom is similar to a king (Chosson domeh lmelech).
The Pirkei D'Rabbi Eliezer lists a few points where we see similarities:
We praise a groom during the week of festivities
The groom wears honorable clothing
The groom must feast
He may not go out unaccompanied
His face shines like the sun.
We find this parallel to a king is taken further by later sources. For example, some Rishonim source the prohibition for a groom to work from the fact that he is like a King.
My question is: Why? What is it about a groom that is comparable to a king?
I'm looking for an answer that will explain the underlying root of similarity, not symptoms in how this is expressed.