Why did Jesus say he ate with tax collectors and sinners?

Answer: He came to call sinners

When the Pharisees objected, Jesus said, "I desire mercy, not sacrifice. For I have not come to call the righteous, but sinners."

“When the Pharisees saw this, they asked His disciples, “Why does your Teacher eat with tax collectors and sinners?” On hearing this, Jesus said, “It is not the healthy who need a doctor, but the sick. But go and learn what this means: ‘I desire mercy, not sacrifice.’ For I have not come to call the righteous, but sinners.””— Matthew 9:11-13 (BSB)