It's typically bad practice to undermine the intelectual base. Perhaps those people don't the company directly, nor do they have the social pull to impact company culture.
And yet, when undermined, the problem becomes exponential, starting with a few bad actors and spreading like wildfire.
Its not a brain drain issue, smart people find ways to make money where conditions and pay become less than ideal.
The most common way of doing this is to seed various leads into competitors for mutual gain. It's not rare to see this - in fact, its openly discussed, out loud for all to hear. Top brass is hopelessly unaware or just doesn't care.
It's so widespread that, this cancer is beyond cure. So deeply imbeded are the parasites that to "cleanse" would involve creating an entirely new company from scratch. In this sense, the relationship is at best symbiotic, yet not substainable - and a long grueling rot grows ever so slowly within.