IMHO it's just preference - at least the last 15 years - but now propagated as a sort of common default/standard with the advent of auto code formatting tools. C# still does what you say (and practically always did - but the Mono people formatted it differently) while Java and JavaScript do the other. Before Prettier, I formatted JS code like C# - I thought it's nicer. Now I use the other because that's what Prettier does and it's usefulness greatly outweighs my preference.

Putting braces on the same line is the K&R style, which predates Allman style with braces on separate lines.

(The original K&R style had the opening brace on a separate line for functions, but I believe this is due to the original syntax for declaring argument types - if you declare them on separate lines, like variables, a distinct { clearly ends the argument block and starts the function body.)