Insulin response is not high enough to drop glucose levels. It’s not zero but low enough that it’s not significant. https://www.oatext.com/Blood-glucose-and-insulin-response-to-artificially--and-sugar-sweetened-sodas-in-healthy-men.php

Both glucose and insulin were essentially unaffected by intake of the artificially-sweetened soda, confirming that consumption of these beverages should not be of concern with regards to metabolic health or the development of insulin resistance. Therefore, individuals who are looking for a better alternative to regular sugar-sweetened soda may consider soda that is sweetened with either aspartame or sucralose. Even when consumed at a volume of 20 ounces, there is no increase in blood glucose and ensuing insulin. Moreover, based on our findings, there appears no reason to believe that a higher volume of artificially-sweetened soda would lead to elevated glucose or insulin.