Surely any 10 year old is savvy enough to find them.
Maybe Pocket Code fits your idea.
The reason why you don't see this advertised for mobile devices is for much the same reason that you don't see programmability advertised for modern computers: it is a feature that only appeals to a tiny subset of the market. The reason why you see programmability advertised in a calculator is due to its utility for the target market (e.g. programming is often introduced in math class).
That's long gone. There's no such tools (that I'm aware of) in the mainstream for smartphones or even computers. You say two things: "they support so much more than TI-basic", well yes and that's the problem. They are developer's tools, not user-programmer tools. If you want to write a quick program to help you in some task you don't have a quick BASIC-like tool to do that. And you also say "a feature that appeals only to a tiny subset of the market", again a self-fulfilling prophecy. There are no tools for non-technical users to program their devices, so only a minority of users do want to program their devices (or even realise that they can do so!)
Some examples that I can think of: Automator, AppleScript, Swift Playgrounds are all intended to be accessible to end users. Spreadsheets typically provide programming-like constructs (without resorting to lower level scripting). There are versions of BASIC for most platforms (including Android and the Nintendo Switch). The last time I looked into it Smalltalk (via Squeak) was still being maintained for computers and it looks like there are Smalltalk implementations available for Android.
While it can legitimately be pointed out that most of these options have to be sought out, they are a subset of what is available. While I agree that people not realizing that their devices can be programmed is a hurdle, a large number of people do realize that it is actually software that controls the operation of their devices yet have very little interest in writing their own programs.
I believe that devices are at least as accessible today as they were in 1981. Today's systems are phenomenally complicated, but you can start making them do stuff with virtually no extra parts. The web browsers are free. Tutorials online are free. Way better resources these days.
Do they expose everything? No.
Are they good enough for learning purposes and basic coding on the go?
More than enough.
Okay, so where are the options that only support basic math and graphics?
Ironically, in the smartphone era, devices aren't even supposed to be programmable anymore (to the end user). They're simply means of consuming content (and a way to be surveilled). The idea that a computer is a programmable machine has all but disappeared from the mainstream.