but I still haven't figured out how jabref is of any help over simply using vim
JabRef have many advantages over use a plain text editor, just take your time to discover it. Indeed one is download several references at once from some site like PubMed searching some words (e.g.
Ivermectin 2021) or individual codes (e.g. a PMID or a DOI) with the Web Search form. Other, already answered, is the New BibTeX entry with a ID-based entry generator to import single references by DOI, ISBN,PMID, etc., or the more artistic New Entry from plain text, mostly for references without any available code, or copy-pasting bibtex code for webs that allow retrieve citation in this format, without the risk of accidental damage the code of another references (e.g., copy-pasting with vim in the wrong line).
But there are much more that just import facilities. Some that that I find very useful are the automatic bibkey generation with consistent patterns, management of duplicate references, sorting, mix local data with those obtained by DOI (e.g., a local reference with issue number without volume and pages, while the DOI retrieve volume and pages but not the issue number), sorting by author, date, key. etc., like in a spreadsheet, switch full and abbreviated journal names of knowed journals,select a bitex/biblatex database offer give according types of references and fields (e.g.,
date for biblatex but only
year for bibtex), see a preview of the edited reference, check if any latex document is actually citing that reference
Others worth to mention could be set score and priority for each reference, groups, export to several formats, send cites to external programs (including vim), fields contextual menu to sanitize entries (normalize names, change case, convert between HTML, Unicode and LaTeX, protect terms), wtc.
But above all, specially for novices, Jabref prevent you from syntax mistakes. It is easy forget some brace or a comma between fields editing in plain text and this will by a pain to debug. Jabref not only write always correct code, but also well formatted (fields left aligned) so is more readable in a text editor and you also test the integrity of the file (Crtl-F8) to detect some problems could pass unnoticed editing in a text editor.
Said all that, the good news is that you can switch from JabRef to vim or any text editor and go back to JabreF without problems. I edit frequently the .bib files in as plain text in the editor text, simply because some tasks like search and replace in many references is more comfortable in the editor (less use of mouse, emerging windows, etc.) or just because the editor is already open and I do not like open one program more.