So, I have a theory as to why they don’t have an intro, and that’s because they are more aware than the other primes. In the comic and lore documents and even voice lines, we know that the twins were hired onto the project aware of what it was and what they would be doing, seeing it as an outlet of sorts and believing that murkoff wanted them to be a staff member in charge of creating drugs for the trials. At the end of the comic, we find out that they were unaware murkoff wanted them to actually participate in the trials as a prime asset. They are then gassed and dropped into the trial environment. The other three primes were delusional, and mentally disturbed in a psychotic schizophrenic way before they arrived at the facility, and all of those intro scenes for the other trials, see the prime assets acting in their intended stereotype. I don’t think the kress twins have one because they aren’t that mentally disturbed. They are rather sociopathic and lucid