Rx Tx Info wrote:

"The forum is abandoned and Clear is not given any support"

This is very sad news for me
After all, I used version 5.x and 6.x for a long time, and I had the best impressions of ClearOS.

Why did this sad event happen, what was its reason?
And what distribution should I use instead of ClearOS now?

There is at this moment not a good replacement for ClearOS, but there are alternatives.
Since you are using 5.x and 6.x you can set up you ClearOS 7. Despite is EOL and there will be no future updates it is solid and stable distro.

It is pure what your demands are to determine the distro that fits for you