Thats the native nature of Magento Itself !
When we have configurable product its generates simple product based on their configurable options and that simple product not displayed at frontend And those products urls are not adding in sitemap.xml file and that's why google also not crawl those products(SKUS) .
it will only crawl configurable product in this scenario.
So if some one google your product directly with part number , they will get the result as Configurable product and then you need to select specific configuration options from there.
But still as per Magento standard if we have this kind of product we must need to go with configurable product rather than creating simple product !!
if issue solved,Click Kudos & Accept as Solution