The elsevier LaTeX class has a couple of options that influence the appearance of the paper.

If you see very large margins and double spacing, then you are using the class with a setting that is supposed to make reviewing the paper easier. It allows the reviewers to add notes to the paper "in site", i.e., directly where they belong. This is especially helpful when correcting grammar and spelling.

The style of a LaTeX document can be changed by simply replacing a few words in the document's source code. For example, an option to the elsevier document class will remove the double-spacing. So it is not unreasonable by the journal to ask you to use that style, even if you think that it is ugly. All these changes should be done automatically, although in a few cases it may be necessary to add a few hyphenation patterns or break formulas a bit differently when changing the appearance. Also note that the publisher has an own version of the class file that is not publicly available for final versions of the paper. If you use their provided style, then it will be easy for the publisher to use this alternative style file, so that the final result looks as intended.

The elsevier LaTeX class file has a couple of options that influence the appearance of the paper.

If you see very large margins and double spacing, then you are using the class with a setting that is supposed to make reviewing the paper easier. It allows the reviewers to add notes to the paper "in situ", i.e., directly where they belong. This is especially helpful when correcting grammar and spelling.

The style of a LaTeX document can be changed by simply replacing a few words in the first few lines of the document's source code. For example, an option to the elsevier document class will remove the double-spacing. So it is not unreasonable by the journal to ask you to use that style, even if you think that it is ugly. When changing the look of the paper, it may be necessary in a few cases to add a few hyphenation patterns or break formulas a bit differently when changing the appearance, though. Also note that the publisher has an own version of the class file that is not publicly available for final versions of the paper. If you use their provided style, then it will be easy for the publisher to switch your paper to this alternative style file, so that the final result looks just as the other papers in the journal.