The whole system behind eMail (all the protocols involved and all the software implementing it) has been built by FOSS and non-FOSS, commercial and non-commercial entities.

Over the decades there were enormous amounts of money and enthusiast labour on it.

And still it's really hard to make sure that the address in the "From:" field is actually the one that sent the email. And if you try to do something trivial like sending an encrypted message to a random email user, chances are almost zero that that user is actually able to read the encrypted email, because it requires additional configuration.

There were >40 years of time, millions of man hours and billions of dollars have been invested in the eMail system, and yet trivial things that pretty much every major messaging service has are still outlandish for eMail.

And not even Gmail, with all their money, managed to fix these issues.