It's likely a combination of some of the hairs not being removed permanently (which is just the laser experience) combined with some hairs being in the wrong phase. It also depends on skin/hair type. And in the US, some IPL services incorrectly label themselves as laser.

Despite that though, it absolutely does do permanent reduction. So in Australia (where laser is much cheaper than the US), lots of folk tend to go for laser first, and then follow up with electrolysis to finish it off, because that works out cheaper and quicker than doing electrolysis for everything