the 2017 redistributable checks for the Product GUID to see if the redistributable has already been installed. It will not install it if the Product GUID is there. If the vendor of the redistributable (MS) changed the Product GUID then the setup prompts for installation.

For redistributables updates MS has a new "in-place" upgrade method. In this case, the Product GUID for the component changes and the new redistributable upgrades the old one. It's very well possible that this is the case here. I'll investigate it.

Update: we'll make a new VC++ 2017 redistributable and include script available with SetupBuilder 2018 Build 6100.