What actually matter is not the actual price, it's the trend.
If the price is stable or rising, the adoption increases. People and businesses get more confident in bitcoin and start using it. More miners start up their gears.
If the price is falling, people get scared / suspicious and will go away from bitcoin.
Well said. Even me only got interested in Bitcoin because the price is high and 1 Bitcoin if you convert it to fiat you can buy a lot of things with just one. The adoption greatly increased because of its popularity, and it's popularity bloom because of its high value. Even in the third world countries Bitcoin has becoming well known. Slowly people are adapting to it and aware of its potential to grow and it's threatening power to fiat money.
Why do people invest to something and willing to risk big amount of money??
Answer: value
Of course many investors are chasing to collect Bitcoin because it is almost as good as gold when it comes to store of value and increase of value through time, like you said when Bitcoin losses its value, many investors will go away.
The price always matter in everything especially with it comes to these things ( fiat, cryptocurrencies, oil, gold ). Without these prices these things will be just like nothing and feel like we're just chasing a ghost.