This is again under the assumption that lightspeed ramming turns things to swiss cheese or whatever. But the way it’s depicted in the film it doesn’t seem like the lightspeed is necessarily the most important element to what would be massive destruction from the collision anyway. Why didn’t the Naboo fighters lightspeed kamikaze? Well why didn’t they just plain old kamikaze? Surely that’d cause some serious damage too.
Because to kamikaze is a last resort. Holdo was desperate to see the mission through. The transports couldn’t go back to the Raddus. They were being take down one by one. Also the Raddus is huge: 3,438.37 meters. That’s bigger than Home One from Jedi.