It's very easy to say 'solve the problem', rather than get a jumper but that's not always the case.
I'll give you an example.
A few years ago, we went on holiday, got a ferry to an island, parked the car, and jumped on another ferry to another island.
A week later, we got back to the car and my remote didn't work to open it. I got in with the key, and the battery was completely and utterly flat.
I had no jump leads, no jumper pack and it was late in the evening, we had about 45 minutes before we had to check in for the ferry home.
There was no indication previously that the battery was on the way out, no slow starts, nothing. In fact, it turned out that as my lad had got out of the car, he'd knocked the rear interior light on by mistake. The car has tinted back windows, there's no way we could have noticed it.
Luckily, very luckily, I actually knew someone who worked nearby and he was able to get me going. I blatted around for half an hour before getting on the ferry home and was able to get enough charge in the battery for it to restart at the other side.
The next day, I bought a jumper and a set of jump leads. I've never needed to use them myself since, but I've been able to help a couple of people with flat batteries.
So yes, these do have a useful place in the car.