[gamblor956]

Hypervelocity ballistic weapons have been researched in the real world, and found wanting. It turns out that mass and volume matter more than speed in terms of the damage inflicted. A projectile that is too fast and small may simply pass all the way through the target, retaining most of its energy, while a wider but slower projectile will impact the target and pass more/all of its energy into the target, causing significantly more damage (i.e., like hollow-point bullets).

So really, it's not that nobody had the idea to build hyperdrive torpedoes. It's that they knew they would be fairly useless, and nobody would expect your enemy to kamikaze their sole remaining flagship into yours at hyperdrive speeds when they could accomplish far more damage to the target by simply crashing into it at normal speeds, as has happened nearly a dozen times in the SW movies. Holdo's act wasn't an act of strategy; it was an act of desperation, and worked far better than she expected it to.

[adrianN]

Even if torpedos are ineffective because they pass right through the object (which I doubt, at relativistic speeds), you might want to consider sacrificing a flagship in case someone builds an attack station the size of a moon.

[Retric]

This is space fantasy, physics conforms to the plot not the other way around. Just pick the right technobabble.

Perhaps it required someone with the right force sensitivity to pull off.

Perhaps shields normally block these attacks and they turned them down to conserve fuel.

Perhaps when going past light speed ships normally just pass right on through normal matter. What happened was a never before seen effect based on failing to reach light speed in some highly unlikely fashion.

Perhaps it is reproducible, but requires tuning the shield frequencies. So it only worked do to the long period in very close proximity.

PS: Perhaps it's just a giant plot hole and showed up because someone at ILM showed a cool demo and they had to work that visual into the movie somehow.

[rasz]

mass is less important than speed, E = mc^2