God tends to provide things for a purpose.
From a Pentecostal/Charismatic perspective, and speaking in more general terms (ignoring any inaccuracies about the contents of the Ark):
When God provides miracles, He tends to do so for a particular purpose. He's not some sort of robot where prayer goes in and miracle comes out. If you ask God to perform a miracle for the sake of performing a miracle, He'll probably say no; if you ask Him to perform a miracle for selfish purposes, He'll almost definitely say no - and He can read your mind, so He can tell why you really want a miracle.
When the Israelites were wandering the desert, they had no food or water so God provided them for them through the miracle of manna - and He commanded then to gather only what they needed each day, forbidding hoarding of resources. Once they arrived in the promised land of milk and honey, they'd have no longer needed the miraculous provision of food and water, since their new land amply provided for them - and to ask for the miraculous provision to resume would have been an act of greed, laziness, or distrust in the truth of God's promises about the bountiful nature of their new land.
Similarly, Moses turning his rod into a snake was a one-time event that was performed for fulfilling a specific part of God's plan. The rod itself had no special powers; it was only able to turn into a snake through the active intervention of God.
God could, did, and still does continue to perform miracles, but it's important to remember that these miracles are performed in accordance to His will and purposes.