BGP was designed when participants trusted each other. That assumption no longer holds.
Route hijacking: An AS announces prefixes it doesn't own. Traffic flows to the wrong destination.
Route leaks: An AS accidentally propagates routes it shouldn't. A small network becomes unintended transit.
Path manipulation: An AS modifies AS_PATH to make routes more attractive or hide involvement.
Why it persists: BGP has no built-in authentication. Anyone can announce anything. The protocol trusts what it receives.