Nemesis and Final Frontier are two movies which I betray my Star Trek cred by the fact I think they have good movies IN THEM but they're all over the place with their inability to commit. In Nemesis' case, there's the death of Data, Picard Clone, Romulanness, and motivations everywhere. Insurrection is a bad movie all round but you could follow what was going on. Nemesis is like Prometheus in that there's a hundred questions you never get to ask (let alone be answered) before the next one needs to be.
It wasn't necessary for any in universe reason, nor for any real world reason. It was dumb, cheap, lazy & dirty
Of course Data didn't need to die, it was a piss poor attempt to give a god awful movie some emotional gravitas.
I kind of wish we had seen the TNG crew go through more or less the same sequence of events as the TOS crew. Nemesis: Data dies, saves everybody, blah blah. B-4 gets sent to some secret lab where they resurrect Data. The Search for Data: Picard finds out about the secret lab and the crew has to steal the recently decommissioned Enterprise-E to rescue Data. The Enterprise is destroyed in battle by the Borg, but the crew hijacks the Borg cube. The Journey Home: Some bullshit probe attacks Earth looking for whatever the hell and the TNG crew has to go to the 2010's to retrieve it. Hilarity ensues, especially since Data is all messed up from being resurrected. Everything ends up being okay and the crew gets to all work on the new Enterprise-F, which is the cool Galaxy-class starship from "All Good Things". Box office gold right there. Adheres to continuity, gets the crew off the ugly-ass Enterprise-E, and ENT would have been avoided too--which is of course a good thing.