What else can affect my ranking?

It's been almost a year since I had this problem in ranking. I was hitting the first results of search engine, and out of nowhere, I've lost more than a half of traffic coming from search engine. You might think that I did something wrong, but actually not, just regular things, like writing good content, sharing it on social media, and other stuff. After that, I tried to fix the problem by checking this list:

- Improving website speed, I abandoned a lot of CDN's and external sources to make it faster ( it was fast before too ).

- I disavowed bad backlinks

- get some new backlinks

- created new good quality content + re-created old posts.

- improving SEO in general

And it's not working out, actually, it keeps dropping. I don't understand why?!