Why is Luffy's bounty $3 billion?

Could you elaborate on the reasons behind Luffy's staggering bounty of $3 billion? I'm curious to understand what specific actions or achievements have contributed to this significant figure. Does it reflect the gravity of his crimes, his status as a threat to the World Government, or perhaps a combination of both? Given his status as a renowned pirate captain, I'm also wondering if his bounty is also influenced by his popularity and influence among the pirate community. Clarifying these factors would help me better understand the significance and implications of Luffy's immense bounty.