The reason is that kali drills such as 6 count sinawalli, largo, sombrada and hubud can be learnt relatively quickly so actors can pick them up and learn them for a film scene.
Look at the knife fight at the end of Under Seige with Seagal and Tommy Lee Jones - it's very basic, if you know your Kali, but looks very impressive to someone watching who has not been indoctrinated.
Jeff Imada, from the Inosanto Academy, has been teaching fight choreography for a long time - look at how realistic the fights in the Bourne films are, because Damon took the time to learn them, and he is performing them with expert stuntmen who make him look good.
In the Matrix films they used way out Kung Fu moves and chains, but that was supposed to look unreal as they are in a computer world and have super powers.
Batman uses KFM, which is not a realistic system, but isn't supposed to be - Batman is wearing armour, he's trained to be almost superhuman in his strength and reflexes, and it's supposed to be a unique fighting system he learnt from Ras Al Ghul and then further developed himself.
Look at Liam Neeson in Taken, Karate, Kempo and Jujutsu - and old man, retired, with decades of experience, practically a master - it looks realistic for 2012 as Seagal did in the early 90s.
Movie fighting is meant to be enjoyable - the actors have some training - look at making of the Matrix to see what they went through.
In Sherlock Holmes the Kempo is almost Real, it is based on what we know of Baritsu, what existed at the time, and what Holmes was meant to study - and the fact that Downey has had many years of acting and has studied Wing Chun privately with a Master for a decade (he has the money to!)
Even something like X Men, where they had to learn to use their unique powers in the Danger Room, is based on how a Sensei may well develop students to use new abilities as they evolve through nature.
Wolverine's fighting style is unique to him, but is based on what the writers and directors know about real fighting systems - and they pay master instructors a lot of money to consult and train the stars.
