This is another one of your can/could questions. These are getting tiresome. They both work.
Which one is correct here:
The reason why we have different sizes is because not everyone can/could use the same size.
Are both okay here? What's the difference.
I don't much like "The reason why ..." I would write, "The reason [that] we have ...".
I'm not alone:
How about takes the same size instead of can/could use?