Bass traps are called that because they absorb some low frequency waves compared to thinner panels but below 80hz, not that much. So they are absorbing everything above including mids and highs. That makes the bass sound more prominent and even. Many people have their subs turned up too high to compensate for uneven levels and when you smooth it out, you hear more.
You would probably benefit from having diffusion on the front wall behind the speakers. And follow the suggestions to use REW and look at some of GIKs videos.