Decrease and increase in the price of Bitcoin based on supply and demand that occurs in the market. When the two are unbalanced or heavy on one side Bitcoin will be corrected if more are wasting than buying, and vice versa.
You can explain in a simpler way, it's like; Bitcoin price volatility is affected by supply and demand. The higher the demand for bitcoins, the more expensive they are, and vice versa.
Who can stop or control the Bitcoin network which is decentralized in nature, try to collect Bitcoins if you believe in the long term potential.
The bitcoin network is not controlled by anyone be it government or otherwise, but the strength of the network could become weaker if large miners cannot survive in the industry after the half of 2024 or the next half. This could have happened if the price of bitcoin did not get more expensive every halving, meaning that miners could not cover the expensive operational costs because the reward was reduced.
I don't expect it to happen overnight, but it's a possible risk to consider if you want to become a long-term holder, say in the next 10 to 20 years. If the price of bitcoin couldn't cover the operational costs of the big miners, then surely the network wouldn't be as strong as it is today.