The Programming Puzzles and Code Golf community faced a similar situation. We began with this close reason:

General programming questions are off-topic here, but can be asked on Stack Overflow.

We were using this close reason far too often on "crap", and we decided to fix it. We looked to Stack Overflow for inspiration, and arrived at a new close reason:

This site is for programming contests and challenges. General programming questions are off-topic here. You may be able to get help on Stack Overflow.

We opted not to mention quality, and instead go for a non-committal phrasing. If you browse through the other answers on that meta post, you'll find that one of the popular answers did mention the high quality standards of Stack Overflow. You'll also find my little suggestion at the bottom, which doesn't mention Stack Overflow at all.

The Programming Puzzles and Code Golf community faced a similar situation. We began with this close reason:

General programming questions are off-topic here, but can be asked on Stack Overflow.

We were using this close reason far too often on "crap", and we decided to fix it. We looked to Stack Overflow for inspiration, and arrived at a new close reason:

This site is for programming contests and challenges. General programming questions are off-topic here. You may be able to get help on Stack Overflow.

We opted not to mention quality, and instead go for a non-committal phrasing. If you browse through the other answers on that meta post, you'll find that one of the popular answers did mention the high quality standards of Stack Overflow. You'll also find my little suggestion at the bottom, which doesn't mention Stack Overflow at all.