That’s because it’s the easy way out for those studios. Can’t design the macguffins so they’re interesting to find no sir. They’ve got to be well hidden, but that makes it too difficult for the player and we can’t have that! Better implement the Macguffin Highlighter Pulse™ to lead them right to it!
There are a few hidden gems (I enjoy Plague inc. and Rebel inc. on occasion, for example), but for the most part, the majority of mobile games are mtx-laden cash grabs. So the actual quality is commensurately low because the devs figured out they don’t have to put in real effort to implement gambling and hook addicts.