There doesn't seem to be a free version at all. There is an evaluation version which is meant to tide you over until you decide to buy or abandon ST. It wouldn't be right to promote such an arrangement as a "free version".
The evaluation version is free and it works forever. If the developers were not OK with that, they would put a time limit on it. Since they haven't, that means they're OK with it.
If you use Sublime Text professionally and you get audited/noticed, not having a licence would be a big mistake. $70 is pittance for "enterprise" software, plus I wouldn't want to work with somebody who's effectively dishonest.
If you're an amateur (in the literal sense, not as an insult), then you might be more inclined to pirate it. I guess the developers are savvy enough to realise this, and just put a nag-screen in instead.
Bottom line, some people have the luxury of having such well-paid jobs that open source is a real possibility nowadays. But ST is likely someone's income/living, and shafting the devs isn't cool at all. If you're not happy with this, you can always make another editor, but it turns out to be fairly hard to do (see Atom).