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.
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.
There is only one factor I could be a little bit more afraid of - if a country becomes too dominant, then an event (be it a new tax, a ban or a sudden rentability problem) driving out miners from there could drop hashrate again like during the China ban. However, the US has currently probably around 35-40% of the worldwide hashrate, so in the current situation it would be less of a problem than in 2021, and 60% of the current hashrate would be still "secure enough". But such events could be problematic in the far future when the attack cost has lowered. So I share a bit your concerns about decentralization problems.
But I anyway expect a change in miner behaviour in the next 5-10 years. As electricity cost is about 70% of the
cost of each Bitcoin mined (for the miners) and renewable energy share is growing around the world, I expect to switch them slowly from a 24/7 mining model to a model where they use a wholesale energy tariff (these are becoming more common now) to benefit from very low prices in times of high solar/wind production and thus at least turn off their gears voluntarily when energy is expensive, mining e.g. only 70-80% of the time but to a even lower price than now (< 5 ct/kWh is easy with this strategy, even < 3 ct is feasible. i.e. better than the famous Riot agreement of 3.5 ct). This model is much more likely to be adaptable all around the world (the "
duck curve" is starting to look the same in several countries), so mining could decentralize again due to this evolution. This is controversial and has been disputed by some forum members, but they haven't convinced me that my thoughts are wrong.
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.
