Short-term perceived benefits - and a mixture of machismo and social pressure. Same reason the smoke and/or drink alchohol or drive automobiles.
Mind you, there are lots of ER visits from people who have fallen over - makes you wonder why anyone would stand up doesn't it?
The report itself bears some closer examination.
It appears in The Dawn report, the official (if lay-oriented) publication of SAMHSA - which is an arm of the US Department of Health and Human Services.
The report notes a trend from 2005 through 2009 - suggesting but not actually constituting a correlation. Correlation, anyway, is not causation.
The trend is not shown alongside other statistics, like overall ER admissions and overall consumption of energy drinks, which would illuminate it.
The report only notes the presence of the drink in ER admissions - not the cause of the admission - nor does it relate the quantities of the drink involved (many people admitted for choking may have alchohol in their system but did the alcohol cause the choking or is it that choking is more likely during a relaxed dinner?)
- but there are telling statements.
The report notes that half the admissions also had other drugs in their system - perhaps the other drugs were the cause of the admission?
2/3rds of the admissions were classified as "adverse reactions" but to what?
Considering that half involve other substances, the "adverse reaction" could be to one of them or just a normal allergy.
Perhaps people who engage in risky behavior also partake of energy drinks ... there is no indication that the overall ER admission rate has increased along with energy drink consumption.
(That wouldn't be conclusive - since there are lots of things that could contribute to an increase in admissions - however, considering the report is working hard to show you that energy drinks are BAD BAD BAD, if there were such a correlation I'd have expected the report to make a big deal about it.)
Overall, the report reads like the dihydrogen-monoxide
i.e. it says that there are reports that energy drinks enhance the effects of caffien and include additives that may be harmful when combined with other substances - but does not say which reports or whether these reports are at all credible. Also does not say which substances.
I hope this is not an indication of the general quality of SAMHSA reporting.