People still don't know how to use efficiently LN...
Just an example:
  1. Open a 5M sats channel, could be private or public it doesn't matter too much, in the end.
  2. Do several swaps through that channel in a total amount of 5 BTC, using many swap services (boltz, loop, fixeedfloat, coinos, zigzag, chainmarket etc)
  3. close channel. On the blockchain will be reflected only 5M sats not 5BTC.
Done, you just "wash" 5 BTC.