Britain introduced rules last year, and is tightening them further this year, bringing cryptocurrency adverts into line with other financial products.

You see warnings that investments might go down as well as up, mandated text on all these ads.

The USA has a very absolutist view on free speech though. Are there any restrictions on advertising?

https://www.reuters.com/technology/uk-watchdog-warns-crypto-...

For the same reason we allow it for politics, propaganda, and products that kill people. Money.

The problem is not the advertisements. It's advertising.