Saying a new writer should spend thousands of dollars on their first book because successful writers do so is like saying a kid who wants to win motor races should buy a Ferrari because the people who win races drive them. The kid wouldn’t have any idea how to control it and would be off in the grass on the first corner with a big repair bill.
Sure, if I was making a million dollars on each book, I’d farm out all the editing and covers and spend a bunch of money on advertising, because doing the work myself would make no sense when I could be writing the next book. But I’m sure glad I didn’t do that when I was starting out, or I’d have quit long ago because I couldn’t afford to keep losing money. After a few years and several books, I’m only just about at the point where I think I’d benefit from doing those things.