Keep in mind that if they're not earning much, they're probably not paying any income tax at all, and until they're earning at least $38,700, the most they'll be taxed on their taxable income is 12%.

I don't think that supporting tax evasion should be a primary reason for tipping in cash.

But there are other reasons why tipping in cash is a good idea, such as making sure that the money actually goes to the worker, and knowing that they'll have immediate access to it, rather than having to wait until their next paycheck.

Breezing past your suggestion that workers should do some tax fraud, not reporting your tips also lowers your social security earnings which is going to lower your payouts as well.

Anyone who is doing an unskilled job that receives some component of their tips in cash is already “do[ing] some tax fraud”. Perhaps I am projecting my familiarity with the food service industry onto others; if you were not aware, this is the overwhelming norm with a rate of occurrence approaching 100%.

If you are working a laborious job and you get cash tips, they go into your pocket. Full stop. To assert otherwise is to be simply unaware of the realities. No one scraping by with cash tips is summing them for their 1040. No one.

Not everyone. I agree with you that it's very common, but an guarantee you from experience it's not 100%.

... it's been a while since I've been in the USA, but isn't the Earned Income Tax Credit still a thing? That might also show up if you're not earning that much...