Why is Registeels base stats so low

No, Steel types will forever suck :*(

It doesn't matter, as even with the same stats as it's brethren, it's bulk will be about equal to Steelix, and somehow deal even less damage.

The formula Niantic uses favors certain stats over others. For example, all the Eeveelutions have the same total stats in the original games, 520, I believe. But in GO, their cps vary greatly. Registeel is just another victim.

Niantic did not implement Physical and Special Attack/Defense.

In the main series games, Regirock has stronger Physical attack and defense, but lower Special attack and defense. Regice has stronger Special attack and defense, but lower Physical attack and defense.

Registeel is the balanced one of the trio, having equal Physical and Special stats. Since Pokemon GO only uses the higher stat in calculation, Registeel ends up having lower attack AND defense than the other two Regis.

tldr: Niantic's CP formula screwed it over. (Sortof like Suicune)

I'd love to see them bump the stats up to match the other two Regis, but sadly, I don't think they will.

Only if Niantic actually starts caring about the game and it's gym/battle system.