Question about implied readers

Each fan fiction writer, I assume, writes first and foremost for her/himself, and writes what they would enjoy reading, and/or what turns them on. But the moment they get their story out of the drawer/ hard drive/ tablet, and post it on fanfiction.net or AO3 or whatever, implied readers come into play. To what extent are writers who post their stories influenced by the potential responses of their (as yet unknown, or possibly already-known) implied readers? Do the writers who cheerfully say “I write what I want to write, and if people don’t enjoy it, too bad” deceive themselves to a greater or lesser extent?