It's for charity.
"You asked and all for a great cause. Me and @ArianaGrande will sign a limited number of #STUCKWITHU CDS ONLY FOR 24 HOURS STARTING TONIGHT AT MIDNIGHT," Bieber tweeted, noting that, once again, all proceeds will go to the First Responders Children's Foundation. First Responders Children’s Foundation funds grants and scholarships for children of healthcare workers, emergency medical technicians (EMTs), paramedics, police officers and firefighters serving on the front lines during the global pandemic.
Amazon joined in the action as well, pledging to donate $5 for every download of the song on Amazon Music through 9 p.m. PT on Thursday (May 14) to the First Responders fund (up to $100,000).