My best guess based on personal experience of alcohol abuse and observation of people around me (offline life, not internet) is some combination of these:
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need to feel in control, to a moderately insane degree, combined with fascination with the feeling of being overwhelmed by an intense state of being that feels under our control
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pursuit of the generally weird, shunned, and “dark” things of life
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the laser-like focus you can attain when your mind and some substance are acting in harmony, and with lesser concerns and nagging psychological and physical pain eliminated
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magicians’ typical love of the feeling of power and ecstatic bliss, which comes at the crest of the high, and the ability to switch mindsets and control internal environment using drugs, drink, etc
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we genuinely think we can handle things “normies” run away from in fear, so why not dive deep into this stuff, we’re Special dammit!
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the utter refusal to take society’s word on what’s best for us that has us summoning demons is applied to cautions about drinking too much, or using drugs
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having other factors that statistically tend people towards substance use, such as dysfunctional childhoods, a feeling of alienation from the everyday world, depression, depersonalisation, derealisation, and so on, some of which are made stronger and more unbearable by magick.
All the things that make us good at magick are also things that make the call of drugs, excessive drinking, excess in any form, appeal to us.
Forgot to add, along with control-freakery, we tend to have a lot of impatience, unrealistic demands on ourselves and the world (and people) around us, and perfectionism, these are all things that tend to go with regular alteration of brain chemistry through drink, drugs, or weird sex.
It’s not IMO that we can’t handle the magick, it’s that we don’t like “reality,” so we find ways to change it, and some are faster and simpler than others.