Display is much more botty by nature and also harder to protect, because “search” (as in search ads) is done on the Google platform which has intrinsic bot protection on it (provided by Google themselves), which blocks a lot of known bots. Whereas display happens on other non-Google owned websites, which are unlikely to have the same degree of protection.
Google, along with Cloudflare and other similar “perimeter detection” systems, deals with bots using black lists, which are regularly updated by various organisations with the IPs of “known” bots and bot networks. They use these to remove already known about bots from their system prior to the botnets being shut down which can take a while. That’s fine as far as it goes, but doesn’t detect “unknown” bots, of which there are many being created all the time – this is where Veracity comes in, by using algorithmic, behavioral and AI/ML techniques to find out if something that looks human is actually a bot. Veracity does detect and protect against bots from display ads, but because there are more of them, it takes longer to show an impact on this channel.