CP-ABE Key generation random parameters
You're talking about the KeyGen algorithm of Bethencourt's CP-ABE. The scheme is described in general and this KeyGen algorithm is supposed to be executed for each user secret key request in full which includes choosing new $r_x$ values.
So, your (actual?) concern that different users who have the same attributes could collude is unfounded.

However, a key authority can add single attributes to an existing user secret key, but for this it is necessary to know $r$ (by storing it in an internal database) or a trick shown by Denisow et al. in "Dynamic Location Information in Attribute-Based Encryption Schemes".