What’s the main reason to reverse engineer crafts?

When I ask this question I ask it with a few things surrounding the topic..

My first question is if the craft is fully functional and has trained pilots, what are they waiting for? Is that them in the sky too? Just waiting to use the tech for purpose?

What will the purpose be for ultimately?

War? War with alien races? long Disclosure + “Dear world, we have FTL tech, don’t be mad at us, we can now explore the galaxy! Domestic Travel?

I’m okay with domestic travel and forgiving them for not disclosing in the very first place because my anger will not surpass my curiosities