It's not happening any more often than it ever did -- you're just hearing about it because of the internet. 100 years ago the same kids would have died working in the fields, or carrying boxes in a warehouse, or just doing chores around the house. News of the deaths would not have left the family/community. It has nothing to do with sports or coaches, simply with continuous exertion.
An awareness of family history is your best bet for reasonable suspicion and tests to rule out the problem.
I agree-we had kids when I was in high school die, a boy and a girl from our high school died from what was probably heart conditions. The girl was playing basketball, came out of the game, sat on the bench and fell over, she died almost instantly.
Our twins just had their sports physicals. They require them here every 3 years to participate in sports. They ask a lot of questions about shortness of breath, heart palpations, etc. but don't do specific testing. I wonder how many kids would really recognize these symptoms even if they had them?
Same story, didn't recognize 'till playing basketball as an adult and ended up in the hospital.