[grandalf]

Using A/B testing and then measuring conversion rate skips a lot of useful steps.

A/B testing can be used to increase engagement with the site, which may result in a conversion days or weeks later.

[m4xt3r]

Yes, but those things are impossible to track. If metrics changed weeks later, there is no way of knowing that it was caused by a test you run earlier.

[lucisferre]

It's easier and easier to track, ad retargeting works this way for example. But yes it is still harder to track accurately.