imma guess here:
1. initially there was the thought leadership land grab, where speakers wanted to demonstrate that they were the expert at Swift because it was the hot topic -> more Swift-focussed talks
2. Swift has subsequently and consistently been steered by C++ experts who want Swift to be the default post-C++ choice instead of Rust -> more PLT in community leadership
3. iOS and Android landscape is stable/mature now -> no reward for stand-out "killer app" products