Yea our network has put a lot of work into what actually runs in the browser for this exact reason.
However most networks go for the volume game so it just isn't that important to focus on JS performance. When you can spend time on jamming more expanding units and video into an ad that for the most part still works, that's better ROI than trying to optimize. Things are finally changing now with adblock and mobile usage but there are lots of long-tail shady networks who aren't legit with business practices in the first place (let alone dev) and the big companies just don't care because they're already big and engineering is a committee based process. Part of it is also the fact that there's no accountability in the industry, especially with tech.
I've been pushing for a technical certification process for ad networks (along with data/privacy handling) but it's a long road and won't happen anytime soon.
However most networks go for the volume game so it just isn't that important to focus on JS performance. When you can spend time on jamming more expanding units and video into an ad that for the most part still works, that's better ROI than trying to optimize. Things are finally changing now with adblock and mobile usage but there are lots of long-tail shady networks who aren't legit with business practices in the first place (let alone dev) and the big companies just don't care because they're already big and engineering is a committee based process. Part of it is also the fact that there's no accountability in the industry, especially with tech.
I've been pushing for a technical certification process for ad networks (along with data/privacy handling) but it's a long road and won't happen anytime soon.