It is honestly very common that after shopping online to be on another website and social media and the same products I viewed or purchased will show up. This is a frequent thing that a lot of people notice, but do not quite understand.
Online shopping is much easier than going into a store and looking through everything. Companies like Amazon have almost made it a standard to just ship something to your house rather than driving to stores to find it. Because of this, most of my shopping I do online. The information that these companies get gives them the opportunity to have advertisements to show things that are similar or that other people have bought that I might like.
Even on Amazon, it is normal to add something to your cart and something will pop up underneath saying others who bought that product also bought this, and list multiple other things that they think I might like to buy. This gives them the opportunity to try and sell more of their products to others under the assumption that if many people are buying additional products along with the current one in their cart, that others will buy them as well.
This shows how when I purchase multiples of similar things, online advertisements can use this to target other people into showing them what they think they should buy. By using these cookies that everyone gives them permission to use, we are giving these companies access to our own data.