They definitely could be used in melee! Legionaries are noted in several cases to have used their javelins to stab at riders, though one imagines it’s a good deal less effective than a dedicated spear would be. Some (though not all) pila had handguards, meaning that the Romans took this secondary usage into account when organizing their equipment.

The lead segment sometimes seen on pila is a weight which improves the impact when thrown. In hand-to-hand, it’s… well, just a weight. Just a disadvantage, really.

The bendy bit is actually the iron shank itself! Iron generally bends before breaking, unlike wood, so the long, thin shank itself will often bend all crooked when it penetrates something, making it a bitch to get out.