Several reasons;
Very few shops are going to stock a product, or stick sight unseen, there needs to be something tangible for shops to base their buying off of. Also, like Stewie said, in order to dedicate floor space to POP material.
Secondly, if you’re spending your entire sales day talking about the “QRE10, that hasn’t been released yet,” buyers aren’t inclined to buy current stock, they’ll wait for the newest latest greatest, or wait longer for the current to go on sale. You’re undercutting your own bottom line, which is inordinately foolish.
Lastly, every product/POP preview I’ve been a part of (since 2002) it has been explicitly stated “this info is still confidential-in the works,” and if it wasn’t stated, it was implied. And if it wasn’t implied, we were smart enough to know it wasn’t info for gen pop. The two big names would Even provide dates telling retailers when info could begin to be teased.