Many images in upload directories

I have about 300-350 images in jpg, jpeg, png format on the website in the blog. I want to convert these images to webp format. I used this plugin. I want to delete the original images because they take up a lot of disk space. I don’t know if this plugin can prove it. However, this is not the purpose of the question.

Today we looked into the directory where wp saves images and I found out that if I upload an image to the blog, the image is uploaded to the directory 6-8 times in different resolutions.
Why ?

https://imgur.com/NZAySIl