preflop equity

[BigBiceps]

A 3% edge against 8 people is small, you need MANY hands to overcome the variance.

The pot is almost always giving you 21-1 to see the turn. With 44 what if the flop is 88K. So you have to see the turn, and then even if you get a 4, you are going to get counterfitted by 78 to a K, 7, 8 or a J to the guy with JJ. You could also already be drawing dead to KK. There are many other types of big danger flops like 36J for example with 2 cards suited. ... You make a set on the turn (oops someone already has a set of jacks). ... You make a set on the turn (oops your set card made someone a flush or a straight) ....

99 wins more often than 44.

a set of 9's wins more often than a set of 4's.
99 makes a 1-card winning straight more often than 44.
99 makes a 1-card winning flush more often than 44.
99 wins more often than 44 when there are trips on the board ie. 555.

That is why it is easier to play than 44.