I didn't know this was a thing, but I'd been noticing this phenomenon. I found it extremely annoying that after going to a website to check something out I'd see ads for the same thing. Even for things that I'd signed up to, i.e. Parse, were showing me ads.
Not excluding current clients is a common problem, which is actually technical. Retargeting requires tags placed in multiple places (homepage, blog, marketing automation, and yes - product). Placing retargeting pixels on product pages is often seen as risky, detrimental to product performance or your clients data. I believe the upside from being able to distinguish between clients and prospects outweighs the risk factors (which are quite superficial to be honest). There are other ways to exclude current clients such as custom interactions and landing pages, but that's a longer story.
Who says placing retargeting tags on product pages is seen as risky? I've never heard anything resembling that nor can I think of a reason why that may be. No need to spread more FUD in the ad space.
Product/tech teams raise that concern (logic being that anything could happen within JS) - in my opinion it's more of a product/engineering/marketing conflict than any real logic/evidence behind it.
