What about haircuts, yard work, and any other often-tipped service profession? "How much would you like me to charge your card?" is, and always was in my experience, super common in those areas--and that's the same thing as asking for a tip.
Hell, if you pay cash at a restaurant, "do you want change for that?" is similar.
I think it has always been more or less that way, and that's fine. A button on a screen or a coded question aren't much different if you're paying attention, and not having to do the annoying indirect-etiquette game probably makes life easier/less awkward for people receiving tips.
I've paid cash at plenty of sit down restaurants and never had that question. Almost invariably, when the cash presented exceeds the bill when the server picks it up (instead of leaving a tip separately after paying the bill), the server will say something like “I’ll be right back with your change” in exactly the same way they’ll say “I'll be right back with your drinks” when you've ordered them. Now, this certainly provides an opportunity to decline (or to make specific requests for how the change should be provided, as may be necessary to leave the exact tip you want), but it's not asking that.
I'd actually say it wasn't complicated, until technology like this made the experience awful. Before this tech existed, I don't ever recall being verbally asked for a tip, and if I had I would have thought it to be the height of rudeness. I certainly don't ever recall being asked for a tip while the machine then broadcasts your tipped amount to everyone else in line behind you.
I get your overall point that tipping is a way to make extremely low-wage jobs slightly more bearable, but I'm fine with people pointing out how this technology is ridiculous and not a good thing.
Don't even get me started on the fact that the purpose of tipping is to reward service after you have received it.