I don't see what's wrong with accepting BTC, ton of banks do all over the world and it's already available for a decade via exchanges and services, why wouldn't the banks directly offer this service?

Let's not mistake banks for tax authority, that's unrelated. Tax evasion and money laundering are two very different things, the latter almost always imply that taxes WILL BE PAID in the tax residence of the ultimate beneficial owner, just having money on a remote bank is not money laundering, people laundering money wants to buy properties, assets... you can generally only do so if you paid taxes. You can't buy properties easily if you just hide money somewhere.

To the contrary, someone laundering money absolutely does not want to show crypto as the source of funds as this is the most suspicious and might call for any sort of check. Generally speaking, it's easier to launder money without any crypto involved, you can just chain a few companies with nominees in different jurisdictions and just invoice each other and so-on, all done online without having to go anywhere.

To be clear again, people laundering money DO pay taxes, often a lot to appear as genuine as possible.

The ones that are successful at both money laundering AND tax evasion generally use very complex schemes that involve buying second citizenship, setting-up blurry structures... it's not done at a level of wealth that is Revolut compatible :)