But the question is not if btc will be zero, that is a dumb question, anything that has some sort of usefullness will never go to zero. So your question should be is bitcoin going to have a value? is btc going to be valuable to ppl, and what brings value to btc
It is mostly future expectations
What these expectations are (were) is another question. For the majority of the so-called hodlers it was an irresistible opportunity to earn easy money. That was the primary reason why Bitcoin went exponential in 2017 as its utility consisted mostly in bringing quick profits. Now these dudes are sitting on losses if they were not lucky enough to jump off in time. In this case, it was an expectation of future speculative growth ("buy low, sell high")
For other people, it is Bitcoin's transactional utility which includes staying under the radar of financial authorities. These folks are not necessarily criminals or involved in other shady activities. With a thought-out approach you can effectively use Bitcoin and top altcoins to hedge against fiat devaluations brought about by reckless governments. This is particularly true for people living in countries such as Venezuela
We should not discard either the tiny economy having been built around cryptocurrencies in the last years like online gambling, freelancing, etc. However small it might be, it is still about real use of cryptocurrencies (other than speculation and as a vehicle for value transfer), so these avenues of application give cryptocurrencies value and utility just like any other useful thing in real life