Why do they think that a huge planet could have shot to the core of Jupiter, blasting apart everything there, but by now still not allowing these fragments to have been pulled back in from the effect of gravity?
Don’t know and that is a fair question. Maybe enough kinetic energy was transferred that the fragments achieved escape velocity.
Take New Scientist’s articles with a grain of salt. They tend to sensationalize the news and many articles are of the “sky is falling/end of the world” genre. They do have a decent, sometimes funny, jokes page.