Why is the following not cryptographically secure?

Seed the algorithm with 32 random bytes S[0].

```
S[0] --hash--> S[1] --hash--> S[2] --hash--> S[3] ...
 |              |              |              |
hash           hash           hash           hash
 |              |              |              |
 v              v              v              v
R[0]           R[1]           R[2]           R[3]

```

The hash function is cryptographically strong, i.e. it cannot be reversed.

The outputs (R) comes in 32 byte blocks, R[0] onwards.

Obviously this is far too simple to be secure, but I wondered why.