Of course, I'm paraphrasing this classic: https://www.youtube.com/watch?v=SxdOUGdseq4
Prefix works for variadic operators like the +, - and / in your example, without operator precedence rules to get wrong. And if one can't reliably remember how those rules differ between languages so people wrap everything in parens anyway, what exactly did you gain from rejecting prefix?
I meant in terms of the complexity of the code needed to parse them. In that respect they are clearly objectively simpler. The entire field of parser theory exists entirely because of non-sexpr syntaxes. Parsing sexprs is an elementary exercise.
Ignoring the latter part and only responding to the first: Root is infix, the left side is just implied 2 here.
These kinds of expressions tend to end with a cluster of parentheses, and it becomes hard to identify the beginning and end of each one, and making sure they're being closed at the right scope. Before someone comments "the editor will keep track of them for you", I want to answer that needing a tool to keep track of nested parenthesis might be a sign that such notation needs improvement.
The reason people mostly don't like it, in fact, is because they find it more complex. A simple infix expression - say (2 + 3 - 1) / (5 - 2 + 4) becomes the comparatively more complex (/ (- (+ 2 3) 1) (+ (- 5 2) 4))) - with multiple layers of nesting to parse, operators a large distance away from what they are operating on etc. There's a reason it isn't taught in primary school, and it isn't objectively superior, just a trade off some people prefer because of other benefits they think it brings.