I don't think there is quite an established term for it; I found several:
- "difficulty of envisioning long-term consequences" will turn up occasionally in discussing behavior such as smoking
- "reward obscures risk" is a bit more punchy, but it fails to capture temporal aspect: long-term risk vs short-term reward
- time preference aka temporal discounting is a well established economics notion that discounts more distant rewards (and risks) But it doesn't quite capture the contrast you want here
- "delay disconting" means the same and there are at least 60 papers in pubmed, for this term, according to this one
- PIG -- problem of immediate gratification; this is the self-help/drug-abuse [re]formulation of the aforementioned economics principle
- short-termism; almost exclusively used in business circles
- akrasia [credit goes entirely to Arnon Weinberg for finding this one]; it seems this the philosophers' favorite term.
I'm sure there are more.
After akrasia got mentioned in the other answer, I was pretty sure this gotta be the most used term in phych, because it has quite the pedigree. Alas, it didn't turn out to be so, the number of pubmed publications mentioning it is only a dozen for the base term and about half-dozen for the "akratic" adjective. So I think "delay discounting" is the most used in the psych & health sciences. There's even one paper that explicitly says so, although the paper is written by a management guy.