How come the conversion rate decreases as traffic increases along time?

I have this online shop (wallpapers and wall decals) for about 6 years and looking at G Analytics, I noticed that 4-5 years ago, I had less traffic and conversion rate ranged between 3 to 5%. Along these years, I added more products and got more organic traffic, but conversion rate kept dropping along time, and today is like 0,6 - 1,3%, way too low. Also, the bounce rate back then used to be 40-60% and today is 10% tops.

It doesn't make sense to me: today I have lower bounce rate, more...

How come the conversion rate decreases as traffic increases along time? WordPress ...