One argument for bulky electronics on starships is simply bureaucratic arrogance. That is, the bureaucracy has mandated all sorts of "safety" and "reliability" standards that must be met for a ship to be certified for sale from the manufacturer. Since the Imperium is the largest customer base, everybody builds to those standards so their ships can operate in Imperial space and be bought and sold there.
This would be no different from aircraft or automobile manufacturing today. So, as part of this the requirement(s) for electronics is they have to use bulky, otherwise completely obsolete components that are 'bulletproof." So, instead of say transistors, resistors, and capacitors the size of fine grains of sand these components are something akin to those used back in the 1960's or 70's that have been "improved."
They've been tested for decades and found to be reliable for say a century or more. For the bureaucracy to approve some new component for use takes several decades of testing, and then several more of limited service use to "prove" their reliability.
Thus, hidebound, officious, and plodding bureaucrats of the Vogon-type have held many areas of starship design well behind the technology curve out of extreme conservatism.