I’ve never understood why just storing them in a big pool next to the power plant is a bad idea. The radiation is not a concern because the water filters it all

I’ve never understood why just storing them in a big pool next to the power plant is a bad idea. The radiation is not a concern because the water filters it all out, it’s stable for long periods of time with very little maintenance, what’s the downside exactly? As in literally dig a hole the size of an Olympic swimming pool, store literally all the nuclear waste that has ever been produced (maybe you’ll need a few pools, I haven’t checked), and spend a few million a year maintaining it for the next century or so.