It is a simple yet not easy question to answer: why does bitcoin have value?
Bitcoin has value because it has both scarcity and utility. It is a limited and useful resource. It is important to note that something must be BOTH in order to command a market value, NOT either.
Bitcoin is limited to the software-imposed hard limit of 21,000,000 bitcoin units ever in circulation. It is useful because it allows payment information to be secured by a decentralized computing network backed by magnitudes of raw hashing power. That raw hashing power is energy (electricity) converted into digital utility. Each transaction must compete (fee market) to be included in the next block of transactions which has a limited [block space] due to the block size limit (2MB) imposed on each ~10 minute block.
We can expect both the value to increase and the number of users to increase exponentially so long as the current technology maintains itself and remains both useful and in a limited abundance.
Bitcoin will always retain market value so long as miner nodes are actively contributing their hashing power to secure the network (proof of work).
No, bitcoin value retains its usability and scarcity as you correctly point, even in the inevitable diminishing of hashrate once mining stops becoming profitable, which is a point we are approaching with every passing day.
This doesn't make the network weak, because there are less miners because it has become too expensive for the benefit, so its still to expensive to attack, even with less miners. There will ALWAYS be miners, just not so many since the for profit ones will be gone. This moment is not too far away, sure the current price is temporary, but letter even with higher bitcoin price, the mining activity won't be able to pay for itself anymore. So the last miners will be those hobbysts, enthusiasts or people that somehow have "free" electricity (ie. renewable sources).
If you were expecting significant profits from transaction fees, LN came to get rid of that. Everyone can just stick to 1 sat/B txs and maybe use LN for anything else. The only reason you sometimes see fees spikes, its because people still blind trust their wallets to pick the "best" transaction fee. This is NOT Bitcoin doing it, its your stupid wallet. So don't let it, set it up manually and don't bother for insta-payments unless you want to do LN or an emergency makes you use a higher fee.