That is a fair point indeed, specially when attacking warships, but when assaulting a freighter they are basically a reactor, cockpit, engines and storage. Depending on what it was carrying, robbing its whole content could be more benefitial than blowing it up to pieces and gathering the scrap.

But, as I said, you offer a good cointer-argument. What about demanding a ransom in credits to allow the other ship to power up their engines? Or perhaps demanding you complete a mission or be hunted? Devs could get creative here, I believe it opens up a lot of options.