A test accompanying a bug fix holds value in many ways.
Firstly, it demonstrates to those reviewing the change that the fix is suitable.
Secondly, the presence of a test encourages reviewers to consider what a test does and doesn't cover, sometimes resulting in comments regarding improvements that had not otherwise been considered.
Thirdly, and of most importance in the long term, a test for a bug fix serves to document oddities previously discovered that were for a time not known about.
Tests that go along with bug fixes are some of the highest value tests, but they must be previously failing tests.
I can’t tell you how many times I’ve reviewed fixes with “tests” that are basically affirming the consequent; they assert something that was already true and it turns out they’re not actually fixing the reported bug.
Next bug you find that needs a unit/functional test (e.g. it is caused by a simple error in transformation in one function), write the test first as a table of inputs vs outputs, find it fails, fix the function, and leave the test in. Gradually, the code base will contain unit tests which are useful, people will see they are useful, and other people might start using them too where appropriate.
You are unlikely to persuade them without actually doing what you say is beneficial and exposing others to its benefits.