I am only aware of two person who have ever done it so I doubt I would say things like "when people could do it"
I suppose it works like most miracles: The God who created the universe and the laws that guide it has complete control over the universe, it's laws, and the propeties of everything in the universe.
Given that the miracle of walking on water was rare when it was first done it should be no surprise that it is rare today.
Jesus was asked how he walked on water. His response was to tell the crowd that they did not follow him because they saw signs but because they like to be fed. He told them "not to seek earthly gains, but aim for a life based on higher spiritual values" Jesus soon afterward said to them, “Very truly, I tell you, it was not Moses who gave you the bread from heaven, but it is my Father who gives you the true bread from heaven. For the bread of God is that which comes down from heaven and gives life to the world.” They said to him, “Sir, give us this bread always.” Jesus said to them, “I am the bread of life. Whoever comes to me will never be hungry, and whoever believes in me will never be thirsty."
So this crowd followed Jesus for the free food and not because they saw signs and they were rebuked. Others were rebuked for asking for signs. And at another time Thomas followed Jesus not because he had faith but because he saw physical evidence and he was rebuked for not having faith. The consistent message is that one should want faith and not food, signs, or physical evidence even if food, signs, or physical evidence are sometimes provided. In the original even Peter sank when he was walking on water but lacked faith.
Things to learn from the event:
Jesus walked on water some 30 furlongs (30 eights of a mile or 19,800 feet)
Peter walked on water briefly but sank due to a lack of faith
The event is a lesson on faith more than a lesson on power
