Soran needed more of a personal connection to Kirk, in order for any death resulting from that confrontation to have any meaning. It would give impetus to leave the Nexus to finish a fight.
I'll say this no matter how unpopular it may be... Kirk's death in Generations is essential. It's a century later and Kirk shouldn't be allowed to end up this desiccated bitter old man like McCoy, knocking about moaning about all the change. He goes down ironically, kicking the bucket one day before retirement.
Malcolm McDowell is awesome in Generations, but just that extra added layer of him potentially being this huge TOS-era villain (even if we never heard of him before), who Picard and TNG crew have to close the book on, would make the picture gel better.
So basically they needed to rewrite Soran to be more of an out and out threat in the 23rd Century opening, rather than a victim we feel slightly sorry for during the rest of the film.