[moltensodium]

The adtech industry embraced flash in a big way, youtube was defaulting to the flash player until four years ago. Plus the dozens of flash ads and trackers that were (and still are) placed into many ad networks.

Now that the adtech firms switched to building the browser and the cluster of html5 technologies have matured it's easier to track people natively. That's really the only reason flash went away.

[eddieh]

There was no Flash on the most popular smartphone (before Android took over). When ad tech went mobile they couldn't use Flash. So, ad tech shifted to web tech.