I posit 2 factors.
1. You can readily do it while doing your job. If you're in a factory with both hands building the widget or on a roof nailing shingles. Your hands are too busy; but with IT? 1 hand on mouse, other hand on beer bottle. Sure construction workers aren't sober angels, but they aren't as inebriated as IT.
2. The inherent negativity of the industry. Many jobs are about 'fixing something broken' and tickets and new 0day and we have to patch. Generally speaking the industry is something negative. When dealing with negativity dayin-dayout it takes a psychological toll which nobody addresses appropriately.
When these 2 factors collide, they feed into each other.
edit/ Sorry, didn't figure my posits would be so controversial. downvoted quite heavily.