because storing it in any way is extremely inefficient - the best solution we have is pumped-storage hydroelectricity with at most 70-80% efficiency.
Renewables aren't available 24/7, as they work in cycles in most cases(sunlight, tides, waves, wind - geothermal and hydroelectric is an exception, but latter also has problems with damages to ecosystem, and handling sediment travel along the rivers) - this is the most basic problem with them. Grid demands electricity in a way that does not align with the renevable's production, so you need buffers.
So you need to build both energy storage, and energy generation - both are source of pollutants, and eRoI over the whole lifecycle isn't actually that impressive. It is a way to go though, but we are far off from fully transitioning to it.
if you genuinely have to ask that question, you need to read more about energy before you start discussing it. and especially about modern nuclear reactor designs, and how catastrophe in Chernobyl happened(forced orders from above, basically a human failure)