IIRC, the in-universe explanation was that the D was the last ship in the fleet that didn't have Borg tech installed on it.![]()
In-universe explanation for what? The writers could've easily used that reasoning had it been the E.
I thought it was because the Enterprise-D wasn't part of the starship network that allowed the Borg to take control of all the ships and anyone under 25.
You guys are both correct... kind of. It was explained earlier in the season that all the ships in Starfleet "talk to each other" to quote Sydney, or was that Geordi's other daughter? Anyway, the point was that every ship in the fleet was connected to the Starfleet mainframe which is how the Borg network was able to control them when the beacon was activated. The Enterprise D however was offline from the Starfleet mainframe which is how it was able to avoid Borg assimilation when the beacon was activated.