St. Denis (? to c.250)

A lot of what is known as miracles seems to defy all logic and science. One of the best examples I can think of is St. Denis.
He was born in Italy in the third century and was the first bishop of Paris, France. After encountering pagan priests who were not happy with his conversions, St. Denis was beheaded in c.250 in the modern day Montmartre section of Paris.
Once his head was chopped off, he picked it up and walked with it for six miles, preaching the entire way. Then, St. Denis handed his head to a religious woman and collapsed. A basilica was built in his honor on that very site in what is now called Saint-Denis in the northern part of Paris.
This is probably hard for most people to believe. And who can blame them? Even with his vocal chords severed and lungs no longer attached to his mouth, St. Denis continued to talk.
I'd like to know, why things like that don't happen today. St. Denis is one of the Fourteen Holy Helpers (those saints whose intercession helps against specific diseases). He is the patron saint of possessed people and those with headaches. His feast day is Oct. 9.