Matlab is intended as a way of making the functionality of programming languages accessible to people who haven't learnt to code. Having indices start at 0 can be a common source of bugs for people not familiar with programming, and the whole point of Matlab is to enable people to apply maths they understand to problems they need to solve, without much additional knowledge.
Most of the tasks that Matlab is used for, e.g. physics and engineering, use the convention of indices starting at 1 in most of the literature, so people working in these fields do not need to convert their algorithms by subtracting 1 from everything.
In addition to this, Matlab is short for "matrix laboratory", and in mathematics, the convention is typically to index matrices starting at 1, so it kind of makes sense that they will follow this convention.
Your rationale for why it makes sense to start at 0 is perfectly good, but it's the purpose of a high-level language like matlab to obscure aspects like these that the user does not need to know.
