Why are passwords always reset after a failed form submission?

Question

Passwords

Situation.
1. Register on some new service with a bunch of fields
2. Filled in everything, submit
3. It turns out that something is wrong and after checking / reloading the page, the password and password verification are necessarily reset.
What is the reason for this? Good tone? internal logic? Something else?
It became terribly curious.

Answer 1

the usual security, to be honest, there is no sense as such, it would be better to use ssl everywhere and save the password;
in fact, on a large number of services, the password is not reset.
now it has finally come into fashion to check all fields with ajax