What you describe is more like Blue Origin, where Bezos can just comfortably pump in a billion each year to build up his rocket company.
Paypal sold for 1.5B [1], and Musk just got 165 million.
That's not a lot of money for building a space company, especially while buying into and growing Tesla at the same time.
Musk risked and almost lost everything, with both SpaceX and Tesla coming close to bankruptcy at the same time.
The SpaceX approach of ignoring conventions, building components in house on the cheap, plus Musks drive/vision and capability to attract young and motivated (relatively cheap) employees probably made the difference there. As well as ultimately attracting Nasa funding to develop a commercially viable rocket.