Hard Cracked Soil Raised Bed

[tryno12]

Why is the soil under my black plastic mulch covering the raised bed so darn hard w/ large cracks and fissures?? I water at holes near plant stem daily but it is hard to even get a trowel to penetrate the soil? The plants do great - production fair to very good. The soil is a raised bed mix w/ mushroom compost. Getting ready to order more black plastic to get ready for spring but wondering about the darn hard soil??

Maybe, if it ain't broke don't fix it ??? and carry on with the black plastic mulch?
My only gripe is way too many pill bugs - they just bother me.

I water every day and 1/2 through season noticed the fissures and hardness of soil. Yes it is covered w/ black plastic. I wonder if the garden lime and epsom salts/ ttone/ and other organic fertilizers have created lumping/hardening of the soil after a few(4) yrs?/ Never seen anything like it. I see the ground outside the bed does crack which I see every year but the garden soil/ mushroom compost / topsoil mix in the raised bed I would not expect this. Around some of the plants put the hose to them and the water disappears...........down the cracks/fissures

Thanks
Pete