They're weighing the impact on their future workforce pipeline (and probably hoping this this only represents a ~4-8 year hiccup) against whatever other benefits they can get from cozying up with the administration (whacky regulation land).

https://www.science.org/content/blog-post/pharma-ceos-speaki...

And who knows, with the right wacky regulatory scheme enacted, the workforce impact will be mitigated away. Probably also banking on the size and power of the American domestic economy to still allow them to siphon talent from across the western world to help make up some short falls.