Question about dice roll security

I just created several keys using 50 dice rolls for 12 word seed phrases with Seedsigner.

I thought to myself that there's actually quite a lot of difference between using 50 dice rolls (12 words) and 99 dice rolls (24 words) as far as possible combinations go, and ran the numbers.

Here's the difference:

6^50 (12 words):
808281277464764060643139600456536293376
6^99 (24 words):
108886437250011817682781711193009636756190618412159145257178661061582856912896
2^160 (BTC max addresses) 160bit:
1461501637330902918203684832716283019655932542976
2^128 (128bit):
340282366920938463463374607431768211456
10^78 (atoms in the universe):
1000000000000000000000000000000000000000000000000000000000000000000000000000000

How are 12 words considered secure then when it's so much less than 160bit? I read that something gets stored as 128bit numbers. 128bit is actually less than 50 dice rolls, so that would make at least some sense.

And how come that 160bit is actually so much less than the number of atoms in the universe? I was always told that there are more addresses than atoms.

Could someone break it down for me please?