Because bin is broadly accepted to be "where executable things go". The various Linux distributions can't even agree on where programs should be installed by root, and you're unhappy that bin is not held to literally mean "binary"?
Now, imagine that instead of building an entire OS, you are building an application. An application that contains a "bin" directory. From the beginning it is up to you and you alone what goes in there. Do you put scripts in there? Or would you say add a /bin/scripts dir to your application? You know for organizational purposes. Now imagine that you are a developer on a big ass mess of an application. Now imagine you are not a developer but a user writing scripts against this big mess of an application. Now imagine its not just one application but 4 of them, that all seemed to do the same stupid shit. Now you are me. My life sucks right now.
A script is human readable and editable, a binary is not. Without an extension the only way to tell this is by size, and sometimes thats borderline because i have seen scripts that are nearly 10k lines long. A bash script that is 10k lines long...
Because there's generally no reason for users to care about the language some executable was internally written in, and forcing them to type a file extension (auto-completion is fine on the shell but non-existent in scripts they write) is pointless and annoying. The script has (or should have, anyway) a shebang identifying the correct interpreter (and therefore file type) in the first line. Every modern Unix-y OS that I'm aware of has the file command or an equivalent.
Not having to type an extension? Thats the best you got? It seems to me that one could write a single script that would capture the command, sans extension, and the thing, no? What happens when you make an executable of your script? Well, it disappears from /bin/scripts and appears in /bin.
I have coworkers who were somehow taught that bin literally meant "bin", like "bucket", and therefore use it for scripts, help files, Perl modules, and God knows what else. Now that can be maddening.
Sure sounds like it. I should mention that i am not a software developer, or engineer, or conjurer, or whatever. I am a scientist who uses programming as a tool, who also made a very bad career choice/change 6 months ago.