MacOS – Copying to targets where the files already exist: skip or stop

I noticed that sometimes, when I tell Finder to copy files to a location where some of those files already exist, Finder gives me the option to "skip" those files and then proceeds to copy the rest.

But at other times, more often I guess, Finder gives me the option to "stop" (or to "replace") and there is no "skip" option.

I cannot figure out what triggers either behaviour.

Today both happened within the same hour when I was copying files from an internal disk to an external disk. The first time I could simply drag and drop all the files and tell Finder to skip the files that already existed on the external disk. The second time Finder didn't give me that option.

Any ideas what makes Finder decide to offer or not offer the useful skip option when copying files?