What is to prevent/discourage the network hashrate coming from a few big companies?

Hi all,

I would really like to see a sussinct answer to this question as I have been struggling to answer it. I will give the following justification to explain my point and hope someone can explain why I am wrong:

If mining gets harder every 4 years, then only the most efficient companies can keep mining. The biggest companies will have access to the biggest funds for research and development meaning that the bigger companies will likely 1) be developing their own miners and 2) have access to the funds to entice other miner developers to sell wholesale to them.

I just don't see a way that smaller miners can A) compete with larger miners and B) break into the mining business with each successive halving.

Please please me wrong.

Thanks, A Fellow Bitcoiner