They drank themselves to death on the first go. It's the only explanation.

I'm assuming that's like pure alcohol (as alcohol related stats usually are to negate the difference in drinks), so if he only drank beer of around 5% he would have drank 8700 beers. Say he started drinking alcohol at the age of 16 that averages out to somewhere between 7 and 8 beers a week (or the wine/booze equivalent). While not exactly alcoholic levels, this is above average (depending on where he lived) and an unhealthy amount.