I periodically send an envelope of cash to Mullvad. So far I haven’t had any issues.
Mullvad supports Monero now, you can save yourself the trouble.
Most projects don’t have any issue using bank accounts because they work well. As others have stated some projects do.
How does getting it insured guarantee that the money will make it to its destination? That's only to get it back in the instance of theft. Anyone who's ever had family or friends in third-world countries can tell you firsthand that mailing even consumer goods is a bad idea. Mailing cash is plain foolish.
Would you also argue that email is useless because you can just send a letter? I don’t think “crypto is useless because you can just send cash by mail” is a serious argument, sorry.