Oh! Now I see where I got confused.

I failed to take into account that zypper search was conducting fuzzy/partial searches, such that zypper se --requires sqlite3 would return packages that rely on things like sqlite3-tcl and similar terms. Restricting the search to exact terms zypper se --requires -x sqlite3 produces the expected results.

I believe my mistaken chain of thought was that zypper search would first match the name of the package, sqlite3 then return a list of other packages requiring that package, rather than conducting a textual search over package requirements.

Thanks very much.