Everybody has areas they do not know. Stepping into those areas takes people out of their comfort zone. Sprinkle in a little imposter syndrome and yeah, people can be hesitant to try new things.

It isn't fear. It is discomfort. It isn't specific to front-end developers, it is just part of being human. If you feel hesitant, ask someone to help you out to get rolling. If someone on your team feels hesitant to jump into your area, offer help to get them rolling.