It doesn't have to be a bad replacement for cash. It can actually be a fantastic replacement for cash if we continue building it as one. The fact is, the current BTC devs decided bitcoin can't scale before ever even trying. They were short-sighted, took VC money to pivot to "digital gold", and started spreading the false narrative that it never could have worked.
> Why are you so set on digital cash?
Because until bitcoin is useful to regular everyday people, there won't be enough buy-in to offset the huge exchange rate fluctuations caused by speculators. If that doesn't happen then it will only ever be useful to speculators.
Your above example scenario makes perfect sense if you're a skilled worker from a wealthy country but it's nonsense if you're among the remaining 80% of the people on this planet. Bitcoin can help EVERYONE if we let it. Luckily other coins have picked up the slack.