It's quite easy to get a measurement on your screen. That doesn't necessarily translate to measuring the impact of ad spending.
If I have social media ads, paid search, and retargeting ads all live on multiple platforms, there is undoubtedly interaction among them and the quite-easy self-serve ad tool is likely to show me a simplistic "last click attribution" at best.
Often on Google I see ads right above a organic link to the same site. I wonder if marketing teams count the ad click as a "win" when in fact I was looking for the company because I learned of it via word of mouth.
Most analytics platforms will report on any straight direct line between spend and incremental revenue. The hard part is measuring the indirect part, as you mentioned, but it is possible.
If I have social media ads, paid search, and retargeting ads all live on multiple platforms, there is undoubtedly interaction among them and the quite-easy self-serve ad tool is likely to show me a simplistic "last click attribution" at best.