Well, for one, AV software started to classify any website with its code as 'infected' with malware. Then adblockers blocked their script, and even today their website doesn't load properly with uBlock activated.
Additionally they (or some alternative) may have been able to improve the software and create a simple consent process to avoid being blacklisted.
Not that I am making much from ads either, but it just really wasn't worth it. Affiliate revenue, while small on a grand scheme, was much more effective .