As any corporation, Epic is pursuing its own agenda and cares about their own dominance and their own profits only.

They currently view the spat with Apple as advantageous to them. As soon as this is no longer the case, they will turn around and find someone else to pick a fight with.

They did do third-party distribution of fortnite already, and still do based on the install flow shown on fortnite.com. (as well as the samsung app store) I have to assume they didn't foresee enough demand for an entire store, especially before android 12 added better support for third party app stores.