It's interesting how inconsistently Trek Captains blow up their ships that are about to be captured. Picard tries to do it in 11001001 and Where Silence Has Lease.
He isn't trying to deny the enemy the use of the ship in either of the cases, not principally anyway. Like Kirk always did, he's chiefly trying to bluff the enemy into ceasing and desisting.
In "11001001", he and Riker are the only two people aboard, save for the supposed enemy, so blowing up the ship wouldn't be much of a loss. But since Picard doesn't know
why the ship is being hijacked, he's setting a countdown rather than simply ending it all there and then; the action serves as a means of investigation, then. Sure, he says enemy use of the ship must be denied, but he also believes there are other methods to achieve this.
In "Where Silence Has Lease", the point is that Picard is threatening to kill his
crew, as Nagilum has no interest in the ship whatsoever.
Janeway is in a fundamentally different situation, as everybody she is likely to fall victim to
is interested in her ship and her technology. Picard could easily give the Ferengi, the Klingons or the Romulans an open lecture on Starfleet technological secrets, and the listeners would just walk out bored by all that stuff already thoroughly familiar to them. But Janeway feels she would violate the PD if she allowed the local starfarers to find out how her replicator makes coffee.
Timo Saloniemi