It's amazing to me that anyone who tried to go to a website, then was redirected to an online sports betting site instead of the site they wanted to go to, would be like "hmm, better do some sports gambling instead, and hey this looks like just the website for me". This sort of thing must work on some percentage of people, but it's disappointing how much of a rube you'd have to be to fall for it.
I can't find the reference now, but I think I read somewhere it only redirects when the user got there by clicking on an ad. In that case it would make a bit more sense - the script essentially swaps the intended ad target to that sport gambling website. Could work if the original target was a gaming or sport link.
This assumes that advertisers know how the traffic came to their site. The malware operators could be scamming the advertisers into paying for traffic with very low conversion rates.
It could be targeting people that already have such a website's tab open somewhere in the browser.
Assuming the user opened the website and didn't notice the redirect (this is more common in mobile), then forgot about it and when they opened their browser again a few days later, their favorite gambling website was waiting for them, and proceeded to gamble as they usually do.
