That is largely because a.) cash-outs of early startups are often not all that significant and b.) you don't here about those cash-outs.
Microsoft was Bill Gates's second startup with Paul Allen (the first was Traf-O-Data), plus they'd done several consulting projects as teenagers. Apple was the second startup for Steve & Steve; the first was selling blue boxes, and it made enough to finance the Apple I. Facebook was Mark Zuckerburg's third; his second was the Synapse Media Player, which reportedly got a $2M buyout offer from Microsoft.
Microsoft was Bill Gates's second startup with Paul Allen (the first was Traf-O-Data), plus they'd done several consulting projects as teenagers. Apple was the second startup for Steve & Steve; the first was selling blue boxes, and it made enough to finance the Apple I. Facebook was Mark Zuckerburg's third; his second was the Synapse Media Player, which reportedly got a $2M buyout offer from Microsoft.