To be fair, LLVM wasn't an Apple-initiated project, but one Apple noticed and decided to adopt later on (they hired Chris Latner in 2005; LLVM began in 2000, and had its first public stable release in 2003).

Unlike Swift, there was never a period of time where LLVM only worked exclusively on Apples own OS's or hardware. From the get go, you could run early versions of LLVM on Windows. In Swift's case, Linux support came in 2016, 1.5 years after Swift's initial release in 2014, then Windows support came 6 years later in v5 (2020).

If Apple didn't want to let Swift suffer the reputation of being an Apple-only language they should've invested more into cross platform support much earlier on. Yes, today Apple and everyone else can say, 'Swift is cross-platform', but dig deeper into the history of Swift and its clear that from the get go, Apple treated non-Apple OS support as an afterthought.