My site is losing traffic and I can't understand why..

I have a WP site, I started it in 2017 as a hobby, adding posts from time to time.
The organic traffic was going up slowly but stable.
It is a travel site about Mexico, in total, I have 950 posts.
450 posts are dedicated to cities and mostly have copypasted content from Wikipedia, which I modify from time to time, adding and removing copypasted texts. I can't say those posts are 100% copypasted. No. But I have no idea about the % of original content because I used to modify them from time to...

My site is losing traffic and I can't understand why.. WordPress ...