Opening up the system will only cater to the small group who want to tinker with their printers. This is not really the main demographic that bambu are going after, they are looking more at the market where people want a machine you set and forget, with a high percentage of success. This is the main reason for a walled garden, lots of tech companies do this.
I think people are stuck in the past where they think everything should be open source, maybe in the early days that helps get things moving but as technology progresses this model does payback on the investment put in to make great leaps. You will often find when hardware is opensource the end users are expected to accept a product which isn’t polished and hide behind the OS wall as an excuse to release a part finished product.
MQTT is a great thing to have for me as I can monitor my machine using this on my local network. I do have a X1C and not a P1P.