how can this happen
This has been discussed in several earlier threads when the problem occurred. It’s unfortunate it happened, but it did, and there’s no way to recover them.
For future reference, no one has promised that posts will stay around forever. It costs money to run sites like this, and if there’s not enough support, then they have to cut costs or shut down.
The best way to ensure posts stay around for as long as possible is to support the site, either by buying available products, or volunteering in some way.
You get what you pay for.
Hope this helps,
Fred