Why should I personally pay for the tools I use at work to make my employer money? Should I also buy my own work laptop? My own software licenses? It doesn't make sense.
Then there's also the tax issue, as others have pointed out. I'd be giving post-tax money in a lot of instances, whereas for Google it would have much more favorable tax treatment.
But the biggest problem is that me personally making $1000/year of donations is pissing in the ocean. It accomplishes nothing. A program where every engineer is doing so accomplishes a lot more.
Wait til you hear about the amount of tools trades people have to buy for their jobs!
(Also worth pointing out that some of those tradesmen are legitimate contractors, and own their own tools in the same way that a legitimate software engineer contractor would own their own computer and IntelliJ license.)
Your argument could be used to say that OP should pay out of pocket for server hardware to run their programs that Google uses, which doesn't make sense.
My argument cannot be used for server hardware, because, after all, Google has to pay for that.
Same for this. One individual elective donation to an open source project doesn't do much. A larger system though can do a lot.
Maybe rephrasing my argument makes it more palatable to you: Shouldn't we, the guild of software engineers, take care of our own and pay our sub guild of open source developers? Why would we leave that to faceless companies?
It also amounts to a $1k pay cut for employees, which no one will be happy with. We already capture a small amount of our value add to the company in terms of wages; this would just make that a little worse. And no, there is no fixed amount that goes to salary plus open source contributions, necessitating the same overall net sum.
It is not really different from whether the company pays for your office space, laptop, and health care, or makes you pay for those out of pocket.