if a Bitcoin mining nounce is just 32 bits long how come is it increasingly difficult to find the winning hash? I'm learning about mining and the first thing that surprised me is that the nounce part of the algorithm which is supposed to be randomly looped until you get a number smaller than the target hash .. is just 32 bits long. Can you explain why then is it so difficult to loop an unsigned int and how come is it increasingly difficult over time? Thank you.

Edit: It's been suggested this is a duplicate, this is not. The other question asked if you could run out of nounces, that's nothing to do with my question. My question is about the difficulty of Hashing the exact same 4 billion unsigned int entry loops.
It is not the looping that is difficult, it is generating a hash for each iteration of that loop.  Furthermore, as @Nate pointed it, a miner will likely have to change more than just the nonce.  As more transactions are coming in from the network, a miner will add/swap them into the block they are hashing, presumably based on maximizing transaction fees.  Each time the transaction set is modified, all tried nonces can be tried again.

As for why it gets more difficult over time, that is a core part of the protocol.  Every 2,016 blocks, the target hash re-adjusts so that blocks will take about 10 minutes.  As more hashing power enters the network, the faster blocks are found, which in turn will trigger the re-adjustment after 2,016 blocks.