I suspect you are using OTC blends like Capt. Black, Half and Half, Paladin, Carter Hall, ect. Those blends contain a humectant to keep them fresh while setting on a shelf in a warehouse and dealers shelf.
You may also have saliva draining back into the pipe and making a soggy mess in the heel of the bowl.
You didn't mention how many pipes you have or how often you smoke. A pipe needs at least 24 hours to rest between smokes to allow the moisture to dry out, more if you are smoking one of the OTC blends. The pipes need to be cleaned after they cool to room temprature after each bowl too. A couple of pipe cleaners to clean the smoke hole, the mortice and interior of the stem will do wonders for the smoking experience.
If you have a pipe store (B&M) nearby, they should allow you to try several of their blends.
Please allow me to suggest trying tobaccos from Cornell and Diehl and McCellands. Cornell and Diehl will work with you to try to determine what you like and suggest blends to try. They have sampler packs of several tobaccos in 2 oz. packages. A call or e-mail to them and they will be more than happy to assist you. You may find their tobacco a little dry because all they use is distilled water to moisten them.
There are many blenders out there and thousands of blends that can be found on the internet.
I have no affiliation with any of the above mentioned companies.