I don't think it's that simple. Google needs devs, it's a competitive market. Controlling or limiting the dev supply is definitely a benefit for big tech, but it's a separate benefit. I think competitive pressure on salaries is the top forcing function.
Google & friends have a business where they can turn a $500k engineer into $2M+ in revenue
I think that's really the bottom line here. They aren't overpaying to starve out the industry, although I'm sure they're perfectly happy to benefit from that indirectly
Yeah, I find it really weird that people are seriously entertaining this conspiracy theory, when the more mundane explanation is that, on average, tech workers generate insane profit.