Even if it was known and it did tend to zero I don't see the issue, Bitcoin is divisible, almost infinitely if you count L2s system (e.g. Lightning Network operates on a millistaoshi base unit instead of satoshi). Inaccessible bitcoins mean that the accessible ones are more rare so in a way it benefits other holders this way.
They also serve the network as a form of security bounty, let's say tomorrow we discover a way to break encryption "soon" pepople will be provided with a path to safer addresses but these old addresses, the ones for which a public key is known, act as an incentive to look for such security flaws.
Nobody prevents you from spending and replacing bitcoins, besides maybe the governments that insist on taxing smaller transactions as if it wasn't a currency.
You should ask them why they've generated about 58 million millionaires and 2,700 billionaires worldwide. That's some actual "hoarding" you should be concerned about, instead of concern trolling about Bitcoin.
If you own a deflationary asset/currency which is guaranteed to appreciate as long as the economy is growing (well it wouldn’t if btc became a global currency but that’s another matter) there is no reason for you to invest into anything unless it offers a disproportionately high return (or buy goods/services now if you can delay buying them)
It would just reduce risk tolerance for investors and increase the real cost of borrowing significantly. That’s how deflationary currencies work (we know that based on several hundreds years worth of empirical evidence).
Not to mention you can't have a robust credit market built on top of a deflationary currency.
Imagine you take out a 30 year mortgage in 2025 with 12 periodic payments of .01 BTC a year.
Imagine offering a 10 year bond that will make quarterly payments of .01 BTC. What is the price of this bond? It is just a meaningless question practically.
They also serve the network as a form of security bounty, let's say tomorrow we discover a way to break encryption "soon" pepople will be provided with a path to safer addresses but these old addresses, the ones for which a public key is known, act as an incentive to look for such security flaws.