Subjective value doesn't mean it's just made up, it means it relates to the subject.

So if I have one gallon of water, I will put it to the most highly-valued use available to me (probably drinking it so I don't die)

If I get a second gallon, I will put it to the second-most-highly-valued use (which might be different than your second most highly valued use)

So the value of the water is subjective (it depends on who is getting it, how much water they already have, and what uses that person can imagine to which to put the water)

But it's also objective in that if you knew all the uses of water available to me and how I rank them in terms of the satisfaction of my needs, you could predict how I will use the water, and there is an objectively correct usage of a given volume of water (conditional on knowing the unknowable)

Bitcoin has no physical form and therefore no subjective or objective use. The first unit of Bitcoin I get doesn't allow me to do anything whatsoever, nor does the second, nor does any further amount. It's true that I can sign the chain to create new UTXOs for the next person, but that person also has no use for Bitcoin. The whole thing looks reasonable only in comparison to centralized fiat currency, in which the same drawbacks apply plus a privileged group is allowed to monkey with the system.

A thought experiment: Suppose Satoshi had promised to pay 1 Bitcoin for each Bitcoin mined, and the ledger tracks how much Bitcoin he owes you for maintaining his records, rather than being the "money" itself. Then suppose Satoshi disappeared and it became apparent he would never pay. Presumably the value of these promises would go to zero when it becomes obvious they would not be fulfilled. But, how is that any different from the current system?