1) Because of a general air of disbelief in America (pertaining to the supernatural). Jesus did no mighty work in Nazareth for this reason (Mark 6), even though He had an anointing of the Spirit to do such miracles (Lk 4:18, Acts 10:28). Perhaps if America was not so materialized and dependent on technology, the miraculous would be more prevalent. Miracles in other less civilized areas are much more prominent, because these people are much more open to the supernatural. I saw a video of T.B. Joshua's ministry in Nigeria and was amazed, watching cancers drip out of people and new flesh completely regenerating.  These people believe in the supernatural.  They don't have aspirins and advil to pop with every headache, nor do they have the sophisticated hospitals and emergency care facilities we have.  They are desparate and needy of supernatural help.  Americans are so alienated from such a desparation.  The result of this material and technological advancement has been the lack of desparation for supernatural help, which leads to an undergirding disbelief; both on the receiving end (i.e. people hearing the message of the miraculous and scoffing at it), and the giving end (i.e. people who kind of believe in healing but are apprehensive as to whether they should declare someone healed because the church has so muddied up the message of Christ's will to heal. The unstaggering boldness of Mark 11:22-24 has been transformed into a weakling "Lord if it's your will please heal so and so".) 

2) Because of a lack of commitment to the Great Commision. Signs were promised to follow the Great commission (Mark 16:15-18). However, our zeal for the Gospel is so weak. If we're not actively performing witnessing, then obviously we're not going to have the signs following. Bill Bright stated that only 2% of American Christians actively share their faith. How many Christians do you know who are avid personal evangelists?

3) Because of a lack of zeal for the spiritual gifts. Paul told us to "covet earnestly" (burn with desire for) the gifts (1 Cor 12:31, 14:1). How many Christians are absolutely zealous for the gifts of the Spirit? The answer to this is closely tied to the disbelief mention in #1.

 

I read the book by Richard Casdorph (M.D.) entitled "Miracles", which documented several of the healings of Kathryn Kuhlman's miracles, including X-Rays and other before/after medical tests.  What would a cessationist say to such evidence?  Perhaps they would say, "The first set of X-Rays was a mistake", or "The cancer went away naturally."  These people have decided not to believe in the miraculous.  Abraham told the rich man who asked to be raised from the dead to tell his brothers about the reality of Hell, "neither will they be persuaded, though one rose from the dead" (Lk 16:31).  Skeptics will explain it away every time, no matter what evidence is shown.  Nothing will convince them unless their attitude changes.  You must "believe it to see it", not "see it to believe it".