It is variance and recency bias. Because your most recent bets after wins (and increasing your bankroll respectively) are largest, the loses are largest.
You will, on average, make significantly more if you update your bankroll to reflect what you’re comfortable losing. Update your bankroll daily, up or down, that’s how you make the most and reduce your risk of ruin.
If you’re concerned about variance you can reduce your Kelly %. At 100% Kelly you have a 50% chance of losing 50% of your bankroll. Vs that… at 50% kelly your EV will be reduced by 25% and your risk of a temporary loss reduced by a quadratic function, ie 25% chance of losing 50%. At 25% Kelly your EV will be halved and you’ll have a 6.25% chance of losing 50% (quartic).
Over the long run, at some point, everyone will go on awfully bad downswings. It is guaranteed. There is no way of avoiding it. Mentally prepare for the fact that eventually you will downswing 30, 40, 50% of your bankroll. That might be now, it might be when you have a 50k bankroll, it might be both.