Song purchases, incorrect/non-standard mixes of popular songs. Why?

There are several songs I've purchased over time, from iTunes, that end up being some non-standard or different mix than what we've all been used to hearing. That is, some are contemporary hit songs and it's not ambiguous about which mix and version has been promoted.

This ends up being disappointing; inevitably, I can find those mixes elsewhere. However, I suspect there are other layers to why this happens and I wonder if the Community here may understand the underpinnings of this. For example, is it due to the copyright holders decision. I see this happen on other streaming services, for example -- you think you're getting that hit song mix, but it's only part of it with a lot of variation that was never published. There are many examples of this, but from my discussions with friends, I don't need to list them out here, as it's a known issue.

Thanks!