The glue isn’t used for water resistance, it’s primarily role is to bond the screen to the chassis, so the entire bonded unit forms a box structure . Which is a

The glue isn’t used for water resistance, it’s primarily role is to bond the screen to the chassis, so the entire bonded unit forms a box structure . Which is an extremely strong and rigid structure, requiring very little material (hence the reason they’re used in construction all the time). But getting that strong structure only works if you have good, continuous, bond between all sides of the box structure. Hence the use of glue. Replacing it with screws would require either a huge number of screws to achieve the same quality of bond as glue, or substantially thicker walls to make up for the poor bond between screen and chassis. Each screw then becomes giant stress riser, focusing all the forces applied to the device into the material around the screws. You really get to have devices like a surface that very thin, with huge screens, without glue the screen to chassis, because the screen and its bond are crucial structural elements.