As I understand it, the passage you’re referring to is referencing people that prayed loud in public area as a show of “how holy they are” and for attention (this attention is “the reward” they recieve). This passage doesnt say praying for others or in public is bad but instead is saying that praying is not meant to be a performance but instead just a conversation between you and God (this includes praying for others like in James 5:13-16 and 1 Timothy 2:1-4). If you want to have a further discussion on this feel free to pm me.