Samson was unbeatable in hand to hand combat. He wiped out an entire army using only the jawbone of an ass, so why did the Philistines get 20 or more archers, have them surround Samson, and then simultaneously let loose a volley of arrows? End of Samson. Permanently!
They also had PLENTY of opportunities to kill him in his sleep. Four at least that I know of, while they were trying out weaknesses. But they gave him a verbal warning and WOKE him up before trying to kill him. She yelled: "The Philistines are upon you!"
The same goes for David, Saul actually yelled: "I will pin David to the wall!" ....
That's the type of stupid stuff that people do in movies, but not real life. It allows the 'hero' (I'm using the word hero pretty lightly here, Samson is more of a serial-killer/terrorist) to survive and allows the story to continue.
It's like when the Batman enemies tie you to a converor belt with a saw, or dangle you over a pool of acid... And then leave the room.
(Judges16:8-9)8 So the axis lords of the Phi·lis´tines brought up to her seven still-moist sinews that had not been dried out. Later she tied him with them. 9 Now the ambush was sitting in the interior room of hers, and she began to say to him: "The Phi·lis´tines are upon you, Samson!" At that he tore the sinews in two, just as a twisted thread of tow is torn in two when it smells fire. And his power did not become known.
If she can tie wet/bloody tendons to him while he's asleep, surely they could jab a spike through his head...
This happens three more times.
I short, the reason that they don't just shoot him or kill him in his sleep: Because it doesn't make for very interesting fiction.
Lore - W.W.S.D?