

Because when the telephone system first was developed, all you had were dial phones, which could only send numbers 1 through 0 (10). So every call needed to be addressible using only numbers.
AT&T came up with the numbering system in the 40s…
https://en.m.wikipedia.org/wiki/North_American_Numbering_Plan
There’s nothing illegal about cryptocurrencies. It’s just random numbers and code.
However, those random numbers have actual value, and governments regulate some transactions, particularly ones that cross national borders, to make sure those transactions do not hide a crime or go to individuals who the government has put under sanctions.
Some people of a Libertarian bent get involved in Crypto to keep their governments out of their business. But those laws still apply, no matter what the medium of exchange is, or how much those people whine about those laws.
Edited to add: I missed the bit where OPs question was about Samurai Wallet. Here is some info about them:
https://bitcoinmagazine.com/legal/samourai-wallet-breaking-down-dangerous-precedents
This is from a pro-Crypto online media source, and its bias is obvious. However, it is also from last April. The Biden administration was very hostile towards Crypto. The Trump administration has embraced it, and it would not surprise me if this prosecution disappears in a cloud of “quid pro quo”…