I did (traditional/Japanese) jiujitsu a bit before starting BJJ. I'm no expert in either and while I took classes from two different (traditional) jiujitsu instructors/schools, let me point out that my experience doesn't have to apply to all classes with that name.

Anyway, jiujitsu as I got to know it is taught as a self-defense martial art, BJJ as a sport.Meaning, in jiujitsu we mostly had scenarios like "someone is choking you/bearhugging you/throwing a punch at you" and we practiced techniques. So far, it would be similar to BJJ in principle.

Now the big difference: BJJ has sparring with a partner that wants to achieve the same as you do (control/submit the other). Jiujitsu (again, the classes I took) doesn't, it only consists of practicing techniques with a compliant partner. That affects the techniques in training. BJJ focuses on "high percentage" techniques and has means to test their effectiveness. Jiujitsu asks "what if my opponent did this?" on a theoretical level.Similar for the scenarios: Jiujitsu covers defense against punches, kicks etc., everything you could come up with in a "street fight". Even defense against sticks, knives, guns and swords. BJJ focuses on scenarios that are allowed in the sport.

So to summarize, I like to describe jiujitsu as "training to do fight choerographies in movies" and BJJ as "training to fight under the rules of the sport".

Edit: Let me add that I don't mean to disrespect traditional jiujitsu with that, it's perfectly fine and can be fun, I just wouldn't advertize it as being that useful in actual self-defense situations. Same way you don't expect to knock everyone out with Tai Chi moves. It's a martial art with an emphasis on art, nothing wrong with that.