Umekayem Emunaso is also in third person. I think ItcheSrulik’s response is the reason. Speaking direct is only when we mean to speak directly, as in a request. I think you can find examples in your day to day life where, upon carrying on to someone about a certain good trait, you’ll end up dropping the direct addressing.
Regarding the end of the Bracha, all Brachos start out direct and end in third person. The reason for this that we don’t really know Hashem. As soon as we focus ourselves to Hashem we realize that we can never truly fathom His greatness.
The only exeption to this is the Birchas Hoda’ah in Shmona Esrei, Hatov Shimcha. It seems that through praising Hashem, there is a special strong bond, as it says, Yoshev Tehilos Yisroel.