Well, for one thing, God's word has been completely revealed to us already, and Jesus has come and died for us already.
The need for miracles was never just to make someone well...miracles were used to prove to nonbelievers about Jesus and God. Now that we have that inspired word, there is no need for them anymore.
Also consider the following passage:
Love never fails. But whether there are prophecies, they will fail; whether there are tongues, they will cease; whether there is knowledge, it will vanish away. For we know in part and we prophesy in part.
1 Corinthians 13:8-9
Tongues and prophesying were both considered miracles, and this verse says that they will fail and cease.
If miracles happen today, why aren't people raised from the dead anymore? Why can't water be turned into wine? When someone can present me with solid examples of miracles, of someone being raised from the dead (or someone's limbs growing back after amputation), then I can believe that miracles do still happen. Until then...