Why did Thucydides son of Melesias criticize Pericles’ use of allied funds?

Thucydides, son of Melesias, criticized Pericles’ use of allied funds primarily on the grounds of morality and fiscal policy. As a political rival, he denounced the extravagance of Pericles' ambitious building program on the Acropolis, arguing that it was immoral to utilize money from the Delian League treasury to finance these projects.1

Pericles defended his actions by asserting that because the allies were paying for their defense, Athens was not required to account for how those funds were specifically spent, provided that their security was assured. This political conflict ultimately resulted in the ostracism of Thucydides in 443 BCE, leaving Pericles’ leadership unchallenged for a period.12