Why are my buttons falling out?

So I have had my S8 for a little over 3 years now and I've never had any issues with any of the buttons until recently. Last week the Bixby button fell out which I thought would just be a once off and since I have pressed it maybe 20-30 times (mostly accidental) the whole I've had my phone I wasn't that bothered. In the last couple of days however the down part for the volume button has let go, it is still working and attached at the top but that may end up coming off too. I've had the card holder cases (the ones that close over the screen and have a clip/magnet) the entire time I've had the phone so those two buttons are always covered and I have no clue why they are giving way now. If anyone could tell me why they are falling out or more importantly how to either prevent it from happening or how to reattach them if it does that would be greatly appreciated. I'm not overly bothered if I can't reattach the volume button because I can easily adjust the volume by swiping down from the top and going into sound and changing it there but my main concern is if my power button also falls out.

This is the half attached volume button which I have just been pushing back in each time it sits out.