Aren’t all those examples “day X profitable” startups? As in startups that had a profitable business model from day 1 and it only took them some share of the market to become profitable after an initial loss (usually operational). GitHub was making money in their very first year.

Many startups these days follow the “never profitable” business model in the hopes of being bailed out by angel investors or IPO.

I’d say it’s definitely possible to bootstrap when your profit grows along with your business. Not possible when you burn money every single day forever.