calling all in when behind with outs

[Guruman]

-live home game- $10 buy in with 2 $10 rebuys. top 2 places pay. blinds are 50/100

seceond level and the button has been white hot and is up 6x the starting chips. The rest of the table is pretty much playing for second place until further notice, and button is starting to get pretty cocky since he's pushed some people off of pots recently.

Villain is a decent player who's not afraid to push with a made hand, a strong draw, or as a total bluff if he thinks he can win a pot. He tripled through in the previous hand by getting all in with me and utg. I had QQ, utg had QQ, and villain had AK.

Hero is utg + 1 with A5[img]/images/graemlins/club.gif[/img] and about 2k

preflop:

three bad players have been limping into every pot they can and autofolding if they don't connect.

utg limps, hero calls, mp1 calls, mp3 calls, button calls, sb completes, button checks. ($700)

flop-

J[img]/images/graemlins/club.gif[/img], 4[img]/images/graemlins/club.gif[/img], 2[img]/images/graemlins/diamond.gif[/img]

checked to button who bets $300, called around with 1 fold. ($2500)

turn 5[img]/images/graemlins/heart.gif[/img]

sb pushes all in and has me covered. bb folds, hero...

[Shilly]

You should have check-raised all in on the flop.

[Guruman]

you'll have to pardon my ignorance on what's probably a routine play.

why checkraise all in? As a weird trap/semibluff?

I think it gives you great folding equity, and I would likely use it, but yes, it iw a semi. You think there's a possibility the aces are outs, and add that to all your other outs, its not bad.