shoplifted goods are paid for

It’s not just the maker that is a problem. I boycott the whole supply chain. Indeed I know the shop in the end of the chain loses, which is good enough. Everyone in the supply chain is part of the problem. I’m not going to fly to Israel to sabotage their factory.

it’s literally factored into the price and claimed against insurance.

That factor counts. Of course only in situations where the insurer does not exclude “mysterious unexplained disappearance”. Either way, the effect is favorable:

• uncovered: the merchant loses. The loss on the sodastream offsets profit. The less profitable, the less interesting to continue selling that item.
• covered w/out exclusion: The insurance increases on the demographic of vendors selling sodastream. Insurance premiums cut into profits. There is pressure on insurers to exclude Sodastream from coverage. Store managers time is wasted filing insurance claims, reviewing video footage, researching security mechanisms, etc. That’s not free and also not covered by the insurance claim.

on your other point, I don’t believe you need to use the branded drink mixes

Sure, but for me the trouble and space of having a single-purpose appliance calls for local generic ready-made concentrates of cola and immitation dr.pepper-like stuff. If limited to experimenting with molassas and limes or whatever, it becomes a hard sell.