It's because Western governments do a much better job of legitimizing their corruption or just doing it "transparently" (which makes it okay, you see?).

Best example is registered lobbying. If you have the money, you absolutely can brazenly bribe politicians and not only is it okay, in the United States its been backed by the highest courts as a form of "expression".

Bribing is okay in the West because its not bribing, its legitimized entirely with weasel words like "lobbying" or "fundraising". As long as you're "transparent" about it then its fine.

Relative poverty and enforcement: if a cop accepts a bribe they can lose their job. It’s not worth accepting £20 (or even £2000) bribe and forfeit larger future earnings.

So when bribes do happen it’s for much greater amounts (or nebulous, hard-to-trace things like favours), which rules out bribes for minor infractions.