Caveat: I am not a lawyer.
I understand that asking you to give up ownership of something may sound weird or pushy. Legal documents are scary, and can be fraught with unintended consequences if they're entered into lightly. I hope that I can shed some light on why a project would do so, since I've been through this with several projects I maintain.
You need to permit sublicensing and re-licensing so that if you die, the project doesn't have to track down your heirs to sign off on any license changes. (Sadly not an unrealistic or particularly uncommon situation.) Remember, IP laws do change, sometimes in ways that change the spirit of licenses, or make them insufficient or suboptimal to protect the freedoms that they were designed to protect. That's why licenses like the BSD 2-clause and ISC exist, because earlier licenses were no longer ideal for OSS projects using them.
It is completely reasonable for the project to require that you agree to give them – actually give them, all the way, without res