They have the $15/hour contractors lugging batteries, hell yea they should invest in automation, but unfortunately as you point out the legal environment does not incentivize them to do so.
$15 is already equal to the proposed federal minimum wage under the current administration. They should automate because lugging batteries isn’t a healthy fit for many of the humans that they are attracting at this low wage.
However working in an Amazon warehouse or a McDonald's is? It's not unlikely that a significant number of people lugging batteries at google would be forced to do that since Google would have no reason to hire them the.