We thought long about rewriting our Swift SDK "back" to Objective-C since this decision would also have its downsides like the one you mentioned.
But since we want to maximize our potential user base we went for it and rewrote it in ObjC.
Nowadays many Apps still use ObjC and for a portion of these users, they do not want to deal with the Swift overhead that would be introduced if you add a Swift library to your project.
Apart from that, Swift is an evolving language and will not have a stable ABI for the next year(s) to come, which also was a strong argument for the rewrite.
Still, our new SDK
sentry-cocoa has an awesome Swift API as a result sticking to the naming conventions Apple provides. So someone using our SDK in Swift wouldn't even notice the difference.
There is still more to the reasoning behind it, but this pretty much sums it up.