Maybe its just media interpretation but Iv noticed in all the historical shows and games I've played set after the invention of gun power no soldier is rarely wearing more than leather. I get that now all warfare is fought with guns but even in stuff like the American revolution or British Spanish war swords still played a role. Baeyanates existed and many used small daggers and regular swords. Id assume even just chest armor would help lower the damage that these semi frequent weapons and i don't see many drawbacks. I guess they could slow you down but if it's just chest armor is that lower speed really worth risking death?
There's a lot of reasons behind it. More can always be said on the matter, so if anyone would like to put their own oar in, please go right ahead! In the meantime, OP, as I love plate armour (and plate armour loves you!), here are some previous threads for your reading. Since this is a plate armour discussion, we of course turn to u/WARitter, who has answers in the following threads:
To accompany those, u/hborrgg examines specifically why armour started falling out of use in line with gunpowder.