The code will be easier to read
Moving to C# is not a good way IMHO. We will end with classes where properties are heavily mixed with the logic before actually we see class methods.
With First-class callable syntax available since 8.1, it would now be possible to write it as below, which is much better then string names of functions:
$result = "Hello World" |> htmlentities(...) |> str_split(...) |> fn($x) => array_map(strtoupper(...), $x) |> fn($x) => array_filter($x, fn($v) => $v != 'O');
For me, the most important argument is that the pipeline pattern is a tried and tested pattern, that this RFC builds upon. A couple of examples:
This RFC adds syntax to make using these kinds of pattern much more convenient.
On top of that, there's the argument that multiple modern languages support a pipe operator:
Finally, I've had numerous occasions where a pipe operator would simplify my own code — I have more than a handful real life cases where this would be useful.