Google's site speed check is a great tool for measuring the loading speed of a website. However, it is not always accurate, and it often gives shopify sites a low score. There are a few reasons for this:
Shopify sites are usually heavy on images. This means that they take longer to load than sites that don't have as many images.
Shopify sites are often complex, with a lot of different elements loading at once. This can make the site seem slower to load, even if it's not actually taking longer to load than a simpler site.
Shopify sites often have a lot of code that is necessary for their functionality. This code can make the site seem slower to load, even though it is not actually affecting the loading speed.
Overall, Google's site speed check is not always accurate, and it often gives shopify sites a low score. However, this does not mean that shopify sites are actually slow.