Why is it that a website can’t be “completed” and then left alone for the search engines to find it? There are many reasons, but Google looks for websites where it’s information is fresh and up to date. Google spends millions upon millions of dollars refining its search engine capabilities for its users and we must do our part to keep our websites evolving as well.
That said, SEO has “changed a lot” in the last decade. We’ll often see multiple updates per year from Google, like the BERT update in October aimed at helping the search engine better interpret natural language searches. Has your website been updated to reflect just that change alone? What are the subtlies in which people search for your products? Do the say, “Hey Siri, I need plastic sheeting”? Or do they say, “Hey Siri, I need thick plastic sheeting.” That difference will pull up different websites. In June a change in Google focused on reducing duplicate organic listings on the SERPs for the same site.