wrt t-rex, my first thought was - it may not have a dick, but if you came came face to face with one - you were definitely fucked.
my second thought - it was probably an evolutionary anomaly. it may have been going down the path of evolving into a bird (not uncommon evolutionary path for dinos). mother nature likely decided it was a hot mess ‘holy shit, there’s no way in hell to get this mound off the ground - this behemoth will never fly’, and abandoned the effort. end result? big ass beast with front legs waning, and wings never developing. shear jaw strength and brute force ensured its survival for a (relatively short) period of time.