When the luxury tax threshold is $71.7 million, and you've got $53.5 million tied up in four players, do the math. That's $18.2 million for at least 10 players.
It's hard to build a deep roster $1.8 million at a time.
So when Kevin Martin left in free agency, there were no available funds to replenish. Thus Jeremy Lamb has to play, proven or not. Thus ancient Derek Fisher will be counted on again. Thus rookies Steven Adams and Andre Roberson might have to play before they're ready.
The Thunder isn't trying to win on the cheap. But the Thunder is trying to supplement is stars on the cheap.