Well 1.2.3 has been out for 5 years now so there are less people playing, but there are a few servers that get quite a few people in during certain times of day. Mostly evening though.
As for the open beta. People just dont play it cause its to buggy. Heck it was never ment to be played like a full release. It was a bug test build. It was ment for people to play it and report bugs so the team could fix them. Didnt work out well so we stopped making open betas.