I do this as well. I keep a set for each spec even though I’m likely to only ever use two.
It’s by no means ideal at least from my perspective, but I just treat it like we’ve always done in the past with managing multiple sets. So to be honest I notice very little difference gear maintenance wise other than having to figure out which pieces are better offspec wise when it comes to Azerite traits as its a spec I don’t prioritize as much as my main spec.
It’s definitely a downside to the system and I think we can all agree on that but I don’t see it as a major issue.
If you’re trying to keep using the same pieces for two specs and you’re not liking the cost to reforge them, then you should rethink how you’re handling the pieces and the system itself. You’re supposed to keep multiple items for different setups with different traits. I’ve reforged maybe 3 or 4 times this entire expansion so far while maintaining the ability to play all 3 roles of my class and keeping gear for those specs.