> Isn't big tech in a fierce competition for employees?
It sure seems to be in a fierce competition with employees.
You will find that almost all big tech places various restrictions on employee open source contributions, ranging from the draconian "prohibited by default" at Apple to "usually ok if you assign copyright to the company and use only company-approved licenses" at Google.
Big tech competes for employees through prestige, paycheck size, perks, and interesting projects. Not through open source policies.