Why won’t Brian Cranston and Aaron Paul sign anything related to Breaking Bad anymore?

I’m not sure if this has already been elaborated on here, sorry if it has.

Long story short, I got the chance to meet Aaron Paul and Bryan Cranston over the past week at 2 different events. Being a big fan of the show I kindly asked them both individually to sign a Breaking Bad poster and they both denied. They were nice enough that they offered to take a picture with me and Cranston agreed to sign my small notebook (which I’m still really happy about).

I was really confused both times on why they wouldn’t sign anything related to BB, does anyone know what is the reason behind this?

Thank you!

Edit: it looked like it had to do with items related to Breaking Bad specifically, if I had simple pictures of them not realated to BB I’m pretty sure they would have signed them