Because the first movie was a brilliant movie. A good mix of Cyberpunk and martial arts with a clever story. The second films weren't, they got too pretentious and decided to try and make a story that wouldn't make sense. They also killed all the power of the agents.
See agents in the first movie are ultra powerful bad-asses who you don't fuck with. You meet one, you run. In the second movie they are down graded to just mooks. Seriously, Morpheus is able to take one on top of a truck. The random mooks in the mansion give Neo a harder time then the Smith clones or what any other Agent as gave him.
So they made the all powerful Agents into just mooks. Which gives a large plot hole to the first movie, where it's suggested and made clear what bad asses they are and that no one has ever gave them trouble. When you kill the power of your villains you take away the threat of that villain.
Also the battles where much worse. I didn't like the Smiths take Neo battle. That battle was also silly, turned Smith from being a plausible threat to being a joke. Also there where fewer one on one battles, fights are always better when it's one on one, bad ass versus bad ass.
I also thought the choreography took a nose dive. Way too much use of wire-fu made the fights seem poor. Rather than seeing cool, bad assed kicks and punched, the final battle consists mostly of flying into one another. That's not cool, it's boring.
To put it short, the script, story and fight scenes suffered in the sequels. That doesn't mean the movies where horrible and I still enjoy watching them every now and again but none compare to the first movie. Also I was expecting a much better sequel for the first movie.
