a lot of glue...
is also for water resistance and drop mitigations. people tend to get uppity if they whack the phone down and its stops working with a mysterious rattle from inside.
It doesn't want to be too easily melted either, as leaving it the sun while drinking your California coffee could result in unpleasant leaks leaving to the phone being permanently affixed to your coffee table (making it difficult to put to your ear without spilling everyone else's drinks...)
However, if glue is required, it should be in a form that can be unglued without breaking or contaminating components to the point they are unusable.
There must be a better compromise than this.