Download speed ingame on Android

Is there an explanation as to why exatcly update downloads are so slow from the game client in pretty much every game on Android i ever played that had such a thing. Screenshot is from magic arena but i also had this happen in fantasy war tactics and some other games ( cant really remember the games as they were more try and forget they ever existed type of thing ) By comparison the downloads from play store ale blazingly fast . Is that some Android limitation or was i just unlucky and those particular games had shitty servers. Also why are they not keeping the whole game in play store and doing this weird in game updates ( Probably it costs more but i would love confirmation ).