The security of the Bitcoin is in hands of the few companies, if profitability drops or they find something more profitable to mine then Bitcoin network will be doomed.
I disagree with this logic.
First, if "they" (I guess you mean the big mining companies like Riot, ViaBTC etc.?) find something more profitable, then difficulty will go down, and it will become easier for smaller players to enter mining again. Decentralization in this case will probably grow, although more slowly than in the past due to higher entry barriers.
If the diff drops, so will security - small miners will join but the security will never be as high because this small miners will never be as profitable as large scale miners and the network will be at constant threat of state sponsored 51% attack from North Korea or some other sources because it will not be enough to secure a trillion+ dollar network.
Second, this will be a gradual process. While halvings are unique events, the consequences are different for each miner, depending on its exact business model (e.g. if it relies more on cheap electricity or on other scale effect, on speculation [HODLing] or not, etc.). So the most likely scenario is that if some big miner retires from the business or goes bankrupt this would be first good for the other mining companies as the difficulty pressure will be lower (hashrate will probably grow more slowly), and will help them to stay in the business.
Which means the mining will be even more centralized than today, more power in hands if the few.
This is not good for many reasons, one of which is Government control - possible forcing of OFAC rules on mining company or straight out ban like in China.
In this situation network will again have low security.
There is also an additional point. Bitcoin mining companies are basically server farms. In periods of low profitability, they can diversify their income sources offering servers for other cloud services. This is already been done by most big mining companies, and it is also one of my reasons why I think that if profitability drops there will not be a "big hashrate crunch", but a very gradual process, because bigger miners will slowly dedicate more percentage of their farms to other cloud services once their hardware becomes unprofitable, instead of going offline completely. And that will re-balance with difficulty growth again and again.
Bitcoin mining is done on ASIC's, not on general purpose CPU.
No one in the world needs this power aside from Bitcoin and other, less profitable coins running on SHA-256.