I would suspect it might have something to do with promoted tweets and things which drive traffic to their twitter/website. These sites are paying for the traff

I would suspect it might have something to do with promoted tweets and things which drive traffic to their twitter/website. These sites are paying for the traffic (which then earns them ad revenue) and seem to be happy with the results. I have seen very few ads for purchasable items on twitter, just lots of traffic driving.