My hypothesis: It takes either an 'OP' player (defined as a top-5 player as regarded by the very arbitrary author of this article), the acquisition of cheap, young, stars via the draft (and a 'tanking'-style record to do it), or both.
I only included the last 8 seasons, as prior to that the results are clouded by the entry draft when every team theoretically had an even playing field.

As you can see from the chart above 14/16 finals teams over the last 8 years had a superduperstar or had tanked. The two exceptions being: last year's Miracle Mavs and the 1999-2000 Lakers which can be regarded as one of the best jobs done of building and coaching a roster without tanking or an OP player in SLOE history.
6 of the 16 teams had finished with a <30% win percentage in the 5 years before their title game. The rest had Penny, Kemp, or Zo.
Conclusions? If you don't have an OP player, tanking successfully is one of the only paths to a ring. Though as KuCoach's article pointed out, it's not a strategy without risks.