Basil may have known that he was leaving the Empire in weak hands but he did not leave it to Romanus. When Basil died he left the Empire to his profligate brother Constantine. According to Psellus, Basil almost certainly knew this was a weak choice. Almost half a century earlier Basil should have inherited the Empire as co-emperor with his brother Constantine. Psellus leads us to believe that Basil took over as the sole Emperor because Constantine was unfit to rule. I suspect Constantine’s apathy just made it easy for his assertive older brother to take over sole rule.
Why then leave the Empire to Constantine? Probably the most obvious reason is that it would have been uncontested. Basil had seen enough trouble with revolts in his reign that he may have thought it more prudent to leave the Empire in the hands of someone weak but secure. Perhaps he thought that Constantine had matured, or at least thought that he would not last long as he was already seventy.
Constantine VIII was not a great Emperor and in three years squandered much of the treasure that Basil had accumulated over the previous half century. While the search for Constantine’s successor was rather rushed there must have been something to recommend Romanus. He was prominent in the Senate as well as City Prefect and he was certainly not the easiest choice. Having already married at a young age, they had to dispense with his first wife before he could marry one of Constantine’s daughters. Perhaps Constantine owed him some very large gambling debts?
Romanus was not a great Emperor either, but I suspect that his energy and attention, while flawed and perhaps even foolish, was an improvement over another five years of Constantine VIII. Psellus tends to prefer a strong martial Emperor to a more pious one. It is not hard to imagine Psellus, whose purpose may not have been to write accurate history but a political treatise, exaggerating for effect.