When templates are used many codes are included that in the view of search engines is garbage, additionally, all that code must be processed generating a workload for the server that translates into the loading time and speed of the website, factors of vital importance when positioning a web page in search engines.
In addition, when using templates you can fall into the mistake of buying a template thinking that it is expensive or the number 1 in sales and that is why it will position our page when in fact behind a good web positioning there is a lot of work in optimizing the code of the page and this optimization is the last concern of who designed the template, which is why anyone can sell web templates but not everyone can position your website.
Our recommendation is to be careful with the developers who use templates because they usually sell cheap packages that include SEO, without even having an idea of what is involved in developing a successful website and the work that must be done to position it.