I saw this:
Probability of getting a full house
and the top answer makes sense to me.
However, why can't I also do this?
Pick a suite. $\binom{4}{1}$.
Take 3 cards from that suite. $\binom{13}{3}$.
Pick a different suite. $\binom{3}{1}$.
Take 2 cards from that suite. $\binom{13}{2}$.
So desired hands are $\binom{4}{1}\binom{13}{3}\binom{3}{1}\binom{13}{2}$.
This is much larger than their answer.
Their answer is $\binom{13}{1}\binom{4}3\binom{12}1\binom{4}2$.