At this point it’s a unique aspect of the language, so much so that changing sz to š for example would feel like a betrayal. There are also a few letters without similar sounds in other Slavic languages (ą and ę) so you’d end up retaining those anyway.
Those make sense since they aren't digraphs. But c'mon, comparing Czech to Polish, it's pretty clear which orthography was designed first, and which learned from the mistakes of the other :)
