While I do think miracles still happen, I tend to think that they are mostly "low-profile" these days-- only visible if you're looking for them, and even then not always certainy identifiable as such.
I also think that some of the stories of miraculous occurrances in the Tanach are not to be taken literally-- the flood, for example, or Lot's wife becoming a pillar of salt-- but I also think some may have literally occurred in some fashion.
In my reading, I have not come across any concurrence amongst Jewish thinkers as to why more "showy" miracles no longer take place; and some of the theories I have encountered seem more satisfactory, and some less so.
My personal opinion is this. A good parent intervenes frequently and directly when raising a small child, in order to teach, to give consequences, and to spare them from too much harm; a good parent raising an older child-- a teenager or twentysomething-- knows to back off, let the child make their own mistakes and suffer their own consequences, and to be more discreet and quiet about providing them aid and assistance, so that the older child can learn and grow and thrive on their own two feet.
In the same way, God has "backed off" in His parenting style as the human race has grown and our societies and thinking have evolved. If we are to become mature, both as a species and in terms of our societies, we must be allowed to walk our own ways, and hopefully come to use productively the teaching and guidance that God has provided us in our "younger days."