Other mistake: Beach scene; by the clocks in the control room it's supposed to be just before or at most past midnight (22:52 in Florida, presumably). Explosions nearby, barely past the thick of vegetation, but the team instantly goes to sleep as if they were anyplace safe. To make it more absurd, they awaken in the 'middle of the night' when Polka-Dot Man relieves himself and King Shark tries to eat the rat lady. Cut to the control room, and it's 23:53. It's as if they did not try to move any distance at all. (00:12:35 - 00:29:40)
Other mistake: Javelin already appears amongst the deceased (red layer) on the monitors, but only intermittently, in different shots his status is normal - at the very least he should have the 'critical condition' brown overlay that TDK has. (00:14:00)
Other mistake: Escaping from her captivity Harley kills a dozen people with the javelin in brutal gory ways, but when she gets on the taxi the weapon's golden finiments appear to be spotless. (01:14:00)
Other mistake: Despite being a deadly marksman (only a few minutes earlier in the movie he stopped a bullet directed at him shooting it off the air), Bloodsport snipes several times at the huge kaiju featuring a massive eye in the central part of its body, and never once hits it. (01:51:45)
Other mistake: Bloodsport and the others see the explosions Harley is running from, which are less than a couple miles off. The beach itself should already be lit by the explosions and burning wreckage, which the team couldn't fail noticing as they were approaching. To make the distances more ludicrous, when we see Flag's signal in the control room it's said he's "1 mile north" of them, He's already halfway towards the western isthmus. No reason why it'd take them a whole day to make it to their destination.
Answer: It's a combination of various reasons. Will Smith wasn't available to reprise his Deadshot role, so there was a shift in the story. King Shark was intended to be in the first film, but the CGI was too extensive, so they went with Killer Croc. In this film, they took the opportunity to bring in King Shark as the "monster" character. But, this film isn't really a sequel or reboot. Basically, this is a new storyline with new characters, and many of the previous characters are just not in the film, with no exposition on what happened to them, and they may not even be part of this film's "universe." The fact that some of the actors play the same character in both films only serves to muddle the concept of this film not really being a part of the previous film's continuity.
Bishop73