Why do

[Brunotheboxer]

Front squats work so much better than back squats for me?

I'm about to give up on back squats as they bother my knees and on fronts I feel no pain at all.
My legs get a much better pump too.

[Nugget]

You are probably doing them incorrectly.
Done properly squats should reduce knee pain not exarcerbate it.
Drop the weight right down and concentrate on form. Video yourself doing them and analyse it or ask someone else to.
Make sure you sit back into the squat. You should be breaking at the hips first not the knees.

[BoostAddict]

Front squats force you to sit back more. Learning how to properly box squat can help you learn to sit back with regular back squats. I emphasize properly because I've met like 3 people who actually box squat properly.

[JRob23]

Everyone's biomechanics are different so, not every exercise will flow the same for all. Like in this case...front squats have a better feel to them than back squats. Sure it's possible as mentioned that you could be doing them wrong but, you also have to take into account biomechanics.

With that said, when you say a better pump in your legs...I assume you maybe mean particularly just in your quads? This would be because they're the prime mover in the front squat where as in back squats, the deeper you get, you start to involve more glute and hamstring drive.