I would assume one address with 377k transactions that has seen over 131 million BTC move through it strongly implies it's some sort of tumbler address. I'm not sure why reusing one address like this would make any sense though...

It is more difficult to trace funds through a single node with gazillion transactions. This is part of the laundering scheme. Of course, all such addresses are immediately suspect, but if they pay out to innocent addresses too... It's difficult to distinguish between signal and noise.

Isn't that overcomplicating things though? If tracing is a concern, why not use Monero instead?