When you're starting out, and even more so when you're young, syntax is the issue. Every paren and sigil you have to type or complicated function name you have to spell is one more bomb that could explode. Keyboarding is tedious. Vocabulary is hard.
And on the TI's, most of that is eliminated by the method of input. While you can turn on an alphabetic mode to type characters, and simple algebraic expressions can be input from the calculator face keys, the environment pushes you to browse and explore the menus of library functions. Browsing is fun at any age. It is not the most efficient thing, but programming was never about how fast you can type.
So your syntax error rate goes way down and while some reference and guidance is needed to know how to use a lot of the functionality, you can focus more on the semantics of, e.g., "what is a subscript error?"
Environments that go heavily graphical like Scratch also have this kind of benefit, but the method used by TI-BASIC, which is mostly an artifact of being designed for a limited interface circa 1990, results in source code that looks and behaves similarly to other languages, making it that extra bit more transferrable.
And the functionality is good for drawing things and building up math concepts, although it's not great as a games environment. I remember my older brother making an Asteroids clone on his TI-82. He got it to where it rendered everything, moved and rotated objects, and took input, but he ran out of single-letter variable names to use. I think if he had known to use the built in matrix and list functionality to store object state and do transforms, he would have been able to take it much farther, but there was a lack of guidance on these things in the early 90's.