So sorry about you losing your key.
The problem with banning is the potential abuse it can grant.
As it is, the steem platform already has a lot of people weilding power.
The ability to ban people actually makes the site more centralized than decentralized.
There is a trade off between decentralization and efficiency . The more decentralized we are, the less control there is overall.
Banning the spammers, scammers, etc woyld be very good, but then unforseen consequences could pop up, plus, the scammers and spammers would become smarter.
Like its always said, you are responsible for your own acc, as long as you dont give anyone your keys, youre safe.