The parent comment is describing supply and demand. If Blizzard attracts a larger supply of workers who will accept lower pay and worse conditions because they intrinsically want the job, Blizzard gains leverage. That is exactly why studios like Blizzard can get away with more than “NicheBoringFinanceCo.”
If an “industry’s labour [is] supplied only by those inherently passionate about it” the post says it would “crush wages and working conditions”.
That runs completely counter to the basics of supply and demand in a perfect competition market. It would be market with far fewer (labor) suppliers, who could therefore command a higher wage, not lower.