It’s less about having one physical charger and more about having one charging cable standard so you’re not wanting for one cable when you mistakenly grabbed another…. You can have 50 charging cables and 50 bricks for all 50 of your devices if you’d like. The convenience comes with the fact that they all take the same connector. Standardization simplifies life and actually will make upgrading cheaper because you’re not locked into a proprietary standard.
I can completely empathize with not wanting to update all of your chargers, but as someone who has recently gone through part of it, I’m 110% onboard with everything being unified like this.