This. It made the crew feel like they were making a difference and were unusually strong united due to openly opposing the government directly with stunts like Ennies Lobby (one of the three major WG facilities) while other rookies were just sinking marine ships and stealing crap. Any other reason for sending excess force against them could've just been chalked up to Luffy being related to Garp and Dragon, or having someone like Robin onboard who was a bigger target for the WG, but the first reasons alone are enough. The Nika shit just feels like a needless add-on that takes away from what made the Straw Hats as a collective special before the split up.
Rob Lucci was ordered to kill Luffy before/during Enies Lobby. Even before he targeted the WG directly, he had a hit on him.
in chapter 382 they already accomplished their mission and captured franky and robin, but Lucci holds them back and says "regardless of who is in charge of this unit, we're loyal to the world government" and when spandam asks him what he wants, he says "blood, when we're here, murder is justified."
later, in chapter 404, cp9 is being tailed by chimney and her cat. Spandam asks why Rob Lucci didn't eliminate them, and Lucci says that he only kills who he's been ordered to. Considering he tries to kill Luffy and targets him specifically in this arc, this strongly suggests Rob Lucci was ordered to kill Luffy.
"Before Enies Lobby, no one thought Rob Lucci could lose."
it's a pattern, since the Straw Hat Pirates made a name for themselves in the Grand Line at Alabasta, of disproportionate escalation from the World Government. They literally sent an admiral (aokiji) after him off Alabasta/Jaya, but he was too personally connected and also lazy. Then they try to have CP9 assassinate him. Then they try to have the Warlords tag-team him, but Kuma doesn't really want to and Moriah is an egomaniac who thinks he can do it himself. But the WG did not think he could do it himself.
You can say "oh its because hes the main character" and sure, yeah. if anyone paid attention to this before the nika reveal, that's probably what you'd assume. but it's still a fact that the WG goes after Luffy harder than they do any other pirate. Why they do it? You can argue about that. But the idea they don't go after him hard enough or theyve never gone after him or w/e is just silly in a lot of ways. He's always been pretty much the most targeted. He just manages to get away.