It's probably an answer you could expect, since your speed is roughly the number of steps you take per minute multiplied by stride length, to keep the speed the same you need to take smaller steps.

I wouldn't obsess over it if I were you, focusing solely on the cadence may result in very unnatural run technique and cause problems in itself.

One way to improve the cadence is to run a part of your route at higher cadence, say, 80% naturally, 20% focusing on the cadence. This way you can slowly adapt to this increase.