Shorter answer, with simpler vocabulary:<p>The Earth is basically a solid hunk of rock, with a core of dense metals like iron. Solid rock and iron just don't collapse under pressures or temperatures that are even slightly sane. (Unless they are hollow, have an empty space under them, or are falling down into something less dense - like an undersea landslide does.) Sure, the pressures and temperatures in the middle of the Earth are high - but we're pretty much talking pressures that some C-list college physics lab could maintain for days on end, and temperatures <i>lower</i> than an old arc welder you can buy on eBay could do forever.<p>Stars that actually <i>collapse</i> - not just cool off, shrink, and fade away - have pressures and temperatures inside that are a million miles from sane. We're talking "a hundred-billion dollar atom smasher, that is 15 miles wide, could do that - but only to a speck of dust, and for a trillionth of a second". Vs. a star that is about to collapse has had millions of cubic miles of stuff under those pressures and temperatures, for years.<p>Under <i>those</i> sorts of conditions, atoms get smashed. <i>Really</i> smashed. We're talking the difference between taking a box of packing peanuts and lightly patting 'em down (inside the Earth), and putting that box of packing peanuts into a big stamping press in a steel mill (inside the collapsing star).