Religious objects and statues are not meant to be idols. They are rather “windows” that allow us to see the goodness and power of God. That is why the Easterns call their religious paintings “icons”, which is Greek for windows.
When we honour the saints and the mysteries of God through Rosaries, paintings, stain glasses, or statues, we are not putting our hope in these objects, or expecting power to come from these objects themselves. But through these objects, especially those blessed by the Church, we can meditate on the works and power of God acted through the mysteries represented, or the saints they represent, or mediated through these objects, especially the relics, which have been made channels of God’s grace. It is not the objects we venerate, but the God who communicates through them. Our hope, therefore, is on God solely. Objects are mere channels to facilitate that.
As to why God would use physical objects to communicate Himself? Why not just continue to speak to us through invisible graces? That is because God loves His visible creation and He has made us physical beings. He knows we like visible and tangible objects; we need sensible objects to make sense of the invisible. That is why He incarnated Himself and came to us in Jesus, and He does not disdain the visible reality. He of course can and does continue speaking to us in His invisible mysteries, but He equally does make use of all channels, the visible channels like religious objects, to communicate to us.
Of course, in our ignorance, we can abuse that. We can turn it into superstition, believing in this particular Rosary or that particular statue has power to answer prayers. But that is not our Catholic faith.