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Three is this thing called slab track, and that's essentially what you are talking about, just without any stones.

https://grn.ams3.digitaloceanspaces.com/wp-content/uploads/D...

Truly almost all new lines should be built this way, its simply a far, far better method. Slightly higher capital cost but far less maintenance.

The rocks also need to be able to move a bit for elasticity, and have sharp edges. For that you also replace a part of the ballast every few years. That's hard to do when everything is sealed. Even with such "glue", the lifetime couldn't be eternal, after all.

How does the water drain through them?

Again here's my software mind:

(a) If you fill all the gaps, water can't get in in the first place, and it doesn't need to drain. Abstract out the problem.

(b) If water can still get in, it can also get out.

Except sometimes water falls out of the sky and it needs to drain somewhere.

water snow and ice will readily destroy anything solid, better to drain it away - this is partially why roads need constant repaving