An mid level engineer at Google averages $280k/yr according to levels. A principal mechanical engineer at Boeing averages $170k/yr according to levels. If Google can pay an H1-B engineer 70% of what a non H1-B employee would get ($196k), they can bid up to 80k and still save money.
Since Boeing is going for a high level employee who actually highly skilled, it's less likely that they would be able to underpay their candidate, but even if they could pay their H1-B employee 70% of the market rate ($117k), they only have ~$50k to before they hit the break even point.
Obviously if the person is highly skilled and Boeing actually needs them it would make sense to bid beyond the break even point, but Boeing needs to be more choosy than Google. In that scenario, Google should put every single L4 candidate up for and H1-B because if even one gets their bid accepted it saves them money. Boeing actually has to decide which candidates they're willing to overpay for which will result in a smaller pool of mechanical engineers being put up for H1-B visas.
