There are some that are very hard to find as a single ingredient. Recently I was purchasing a medication for back pain, I had a choice as to which other ingredient I wanted, but I didn't have the choice of none. I picked the combined ingredient I don't like to take, because I wouldn't be adding it on top.

I did toss on the other option, stand alone, at one point so I could get some sleep.

It left the medication I was more comfortable taking as an add-on option if things got bad enough. (This particular medication has much lower risk of overdose, so if I got stupid and took it again there would be no significant additional risk.)

It's ironic, but taking the combined medication with a known higher risk of its own was better than taking the lower risk medication.

One was controlled, higher risk, taken at specific times, while the other was taken in addition, on demand, as required.

Specifically this is one reason they’ll sell you cocodemol or Vicodin but not codeine or hydrocodone directly — if you take enough to get a codeine high, you’ll have taken a toxic amount of paracetamol/acetaminophen, so they assume you won’t.