Because it’s a drug that makes you feel good?

More specifically, its a stimulant that makes your brain more active and helps you cut through your exhaustion. Like caffeine, its a “work drug” designed to crank more units of labor out of you in a limited time span, at the expense of your overall health and well-being.

That’s why capitalist countries have been so loathe to outlaw it, when compared to the creative/transgressive stimulants like LSD and THC.