Raphael Y. answered 08/13/23
Roman History(753 BC-1453 AD)
Unfortunately, not every Roman Emperor has a bust. For Majorian, there is no bust of him. Perhaps, there needs to be more excavation to disprove the notion of no busts of Roman Emperors in the 5th-century Western Roman Empire. If there is still none, it is due to the lack of adept sculptors to make them due to the constant civil wars and wars against the Germanic tribes. Sometimes, the style depended on the skill of a sculptor. For example, if you look at a bust of Theodosius I and Leo I, there is some resemblance of the "realistic style" that existed earlier in the Roman Empire. That referred to when the bust looked as realistic and detailed as possible. The Eastern Roman Empire, or the Byzantine Empire, was safer than the Western Roman Empire, so skilled craftsmen and artisans would go to the East for more safety than the lesser safer western half.
Other times, the choice might have been deliberate, regardless of the art in that time period. For example, there are two busts of Diocletian. One was a simpler version, and the other was more complex. This adds an another point: coexistence.
Another example would be Julian the Apostate due to wanting to return to the Principate period.
An another example would be the time period. From the Principate period(27 BC-284 AD), it kept the realistic style. From the Dominate period(284-476 AD), it became less realistic due to no longer being 'amog equals.' Christianity made the busts more simplistic like Constantine I.