Normal keyboard use either a rubber or silicon as a middle man between the key itself and the board. Whwn u press down on the key the rubber will make contact with the board sending the signal which key is pressed. For laptop that have heat management issue chance of this rubber melting is there. Especially if the heatsink or heating device is around the keyboard

It doesnt fully melt the rubber but part of it that comes in contact with the board. This causes it to stick to the board for a while longer depending on the damage. Most notable is the W key which we use alot