Why is a reform beit din not seen as ok by the orthodox Jews?

It has a mikvah, circumcision, a beit din in the uk at least the only issue is if they’re women or don’t keep shabbat. Now what if you ask for men and secondly if someone believes they aren’t breaking shabbat does it still count as them keeping shabbat since in their eyes they are? Seconding on this, do most reform jews keep shabbat and what about masorti Jews? Thank you.

Also if someone did that and then wanted to be orthodox, would the beit din be less willing if the person contacted the orthodox beit din before the reform one? I don’t believe in female rabbis or interfaith marriage but I’m considering if a reform beit din would do a legitimate c0nversion (trying to avoid the bot!)