What can be the problem of my website?

Hello, i have a website that was built in 2005. It had the 1st position on 1st google page, on my main keyword ( animação de eventos ). The website is in Portuguese and we are talking about google.pt
Recently, new websites shown up and my website started to get down, until getting the google pt 2nd page. This websites almost don´t have any content, some of them have also not finished parts, and i ued several seo check up tools to test mine and those competitors. They all give a much more…
What can be the problem of my website?

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