If they had replicated the mobile emitter

[jo jo]

and all the suips engineers and starfleet inventors would be out of their jobs

 

[jefferiestubes8]

Its 29th century tech, maybe there's some element in there unknown to 24th century people that the replicator can't duplicate.

I agree.
While the replicator can reproduce elements and solids & liquids down to atoms you would think it could recreate complex compound metals in the mobile holo-emitter.
The temporal prime directive does come into play.
If it didn't you would think Janeway would have one created for each shuttlecraft, the Delta Flyer, and for exterior EVA work outside VOY during repairs. the EMH subroutines could have been programmed for repairs as well as piloting shuttles safely when crew were injured or needed to use weapons.
Actually Janeway implemented the Emergency Command Hologram subroutines which effectively allowed the 29th century tech to let him go all over the ship. By not replicating it Janeway kept within the prime directive.

 

[Guy Gardener]

Surely if they can TRANSPORT the mobile emitter, break the bastard down into energy, hold it's pattern during transit and then put it back together again, then they can REPLICATE it... Since the Replicator, holodeck and transporter are all from the same family of technology.

I like the idea that Janeway just didn't want to replicate the emitter because it was sort of immoral to keep the emitter and TOO immoral to massproduce it since that would make her just like Starling.

besides if the Earth hadn't already been destroyed in the 29th century then it's fortunate that the mobile emitters presence in the past created an alternate 29th century, not that Janeway wasn't expecting some one to turn up sooner or later form the alternate 29th century or an alternate alternate 29th century claiming that she was polluting the time line with disingenuous technology.