Economic realities change and things do in fact get cheaper thanks to technological progress or get more expensive due to the one or other scarcity.

Someone posted a graph of cocoa prices that went up 4x over 12 months so there's that. But these things average out a lot and overall change slowly. The technology for brewing beer is buy and large static so there's no reason for prices to change.

No currency has to be perfectly stable, we'll all do planning to the extent that the given stability allows. But your currency that you are proposing has to be as stable or more stable than the one people are using otherwise people won't use it. There is a market of currencies and they compete on stability.

Fiat has mechanisms that grow or shrink the money supply in accordance with a growing or shrinking economy, that's what makes fiat prices somewhat stable. Bitcoin has no mechanism like that and therefore no chance at all to begin with.

If you want to make a more stable currency that can compete in the financial market, then find a better mechanism that can grow and shrink the supply than the one we have.