Didnt implement redirects for what? The prior part of the article doesnt even mention you changed any page URLs.
But if you did, that is most definitely going to have caused problems.
Think about it - the pages are no longer there, so they will get dropped from the search index, so wont appear in search results, resulting in less impressions/opportunities for click-through, and you will receive less visitors as a consequence.
You effectively delisted your sites content. The existing inbound links will now point to non-existent pages, so they carry no "authority" to your site. The content that is on the new URLs has no inherent "authority" so its not being ranked as well as it was on the old URLs. The search engines will rank it lower (e.g. page 10 instead of page 2), so less impressions and therefore less visitors.
You will likely be able to (partially) fix this with redirects - as sites that still link will still bring authority. But you will possibly have lost any history-based authority (that which comes from being a reliable and consistent URL), which may not be able to be retrieved.
I would recommend going through old access logs to find what your old URLs were, and redirect them to the new URLs for that same content (not a wildcard redirect to homepage!)