Probably because the app isn’t available for the os the TV is running. Your best bet is to not buy a “smart” TV unless it’s running android. If you happen to already have a “smart” TV, buy something like the shield and you can run all apps available for android without being stuck with the shitty os on whatever TV you have.

It’s more likely MLB hasn’t developed an app for LGs platform than LG is blocking an app from their platform.