It's just statistically more likely. The UK has a lot of Russians and somehow even those who were notionally sanctioned as Putin's puppets found it easy to obtain special case exemptions or conveniently happened to have transferred key assets to somebody who wasn't sanctioned coincidentally as it happened. Russia being "broke" is a macro-economic idea, the Russians involved are wealthy.

As with the drug trade lawyers are happy to take £££ of your obviously stolen Russian cash to help you argue that you and that money are legitimate. And if you lose? Oops, the payment to the lawyers is magically exempt so they keep that. The incentives to work for people who you know are crooks are very strong, just need to get cash up front because when anything goes wrong they're suddenly penniless and have never met you.

That's the stupidest thing about Trump's lawyers. These guys must have represented crooks before, so he's not different on that score, but why did so many of them not demand cash up front?