My guess is these two reasons: lots of mods and admins fall in that category, plus Big Pharma influence.

Big Pharma is the main reason why it's all but illegal to criticize trans-anything nowadays. Now that they can't sell legal heroin anymore, they need a new huge revenue source. Covid bullshit is drying up soon. But gender bending is HUGEly profitable. It requires a lifetime of heavy medications. Each person who fully transitions is a six-figure moneymaker for Pharma. Hence they have a huge reason to incentivize it.

most reddit admins and mods are LGBTs, specifically trannies

Exhibit A: Owner's wife

Or is that for Rule 3 and zoophiles?

Same way they became a protected class in general--emotional blackmail and threats. As MLGS says,

They're the first social movement in history where their primary tactic is to threaten to kill themselves if you don't give them what they want.