I think in the past they had some sort of republic but they found it flawed. Then they decided to got for an empire. But because there were many factions and no one trusted anyone they decided to go for a truly neutral Emperor. They cloned it from a wide selection of supreme genes (not some nobles genes, just genes of the whole race, further selected by some algorithm). This way they got a person at the top that had no prior obligations, no family, no old debts and favours to be repaid. Truly neutral ruler to who all the factions could agree.
As a bonus such person can be considered a superior human (enchancers, the best combination of genes to make the best intellect, aggressive prunning of inferior genes, boosted immunity system, resistance engineered at the very early stage). No mental illnes, idiots and the like which were plaguing monarchistic systems. A speciment truly designed to be an awesome ruler.
I agree with the infrastructure thing. They need an extensive royal cloning facilities.
But there is no "they", only specific powers and factions.
If the old republic is so corrupt and weak that an empire seems a better option, how can distrustful factions agree on a "truly neutral Emperor"?
In the best case, some factions agree and support the emperor but many planets/systems/colonies where other factions are prevalent revolt, proclaiming some combination of independence and rejection of what they can well consider a coup.
And the best case scenario is unlikely: factions do not automatically erase themselves from existence only because of a new institution like an empire, and they'll try to influence and corrupt the empire.
The traditional way to found an empire is by superior power, possibly through peaceful means. For example, a "superior human" can rise to power by being, well, superior (and benevolent enough to gain popular support), crushing dangerous factions in the process; the emperor, rather than someone with a conflict of interest, can worry about being succeeded by his or her clones.
All it takes to have a superhuman emperor without unrealistic political dynamics is a spark of disinterested effort of a plausibly small scale, e.g. a single visionary scientist and a cloning vat, or even pure coincidence (example: Red Son, a recent "alternate universe" version of Superman where Kal-El lands on Earth at a different longitude and succeeds Stalin as the head of USSR).