Google files 6.5k H1-B applications per yr which includes transfers (https://www.myvisajobs.com/Reports/2019-H1B-Visa-Sponsor.asp...). To assume all of this goes to new employees is misleading since Google has attrition too. So assuming 10% attrition, Google needs to fill in that 10% and add more employees. Your argument conveniently assumes that H1s are only going to net new employees vs. those that fill the gap too.