I'm looking at the SOS features across smartwatches. I'm curious why does the Apple SOS feature require you to swipe instead of simply having buttons to press? It seems counter-intuitive to make it harder in terms of usability in the situation of an emergency where the user might be experiencing compromised physical ability e.g. trembling
"Why was this made like this" is always difficult to answer - for one, we don't know who made this decision and can't ask them, and for another it's not up to the designer to decide whether something has good usability. If it was, we wouldn't need to test our designs with real people :)
Instead, let's look at the effect: Swiping is, indeed, harder to do than just tapping. Crucially, it's more difficult to do accidentally. On many mobile UIs, receiving a phone call while the phone is locked has you do a swipe gesture to accept the call. This makes it harder to accidentally tap an "accept" button while you're just trying to pick up the phone.
Returning to the watch, the swipe-to-SOS makes it harder to accidentally send an SOS when just picking it up. Since you have many options close to each other, it also lets you preview which of the options you have actually placed your finger on before going through with it.
At the same time, it also may make it harder to send an SOS in general. Or does it? In the trembling situation you describe, I imagine holding onto the watch and sliding may be more useful than 4 small buttons onto which you need to stick the landing. Seems like this needs testing with affected users!
With this, we've had some discussion regarding the effect of this decision, and now can make an attempt to answer the initial question: Why did Apple do this?
Apparently, they identified that preventing accidental SOS calls outweighs faster access to the feature.