Realism.  If I write a paper that starts with "airplanes are made to go to the moon", it turns out that you can fly with an airplane, but that airplane tech is never going to get you to the moon.

The way bitcoin was constructed makes it impossible to use as digital cash (note that DASH won't be digital cash either, it is bitcoin with extras: tumblers and mem pool certification - I say this because of the name).
A block chain having each and every transaction ever to be had by the users and proof of work that must be more expensive than the value of what is secured by it, can never be "digital cash".  Moreover, there are monetary parameters (block reward halving shocks, block size limits....) that make that this is not going to be a high-liquidity asset but a speculative asset.

In other words, bitcoin's DESIGN, from the start, made that this was not going to be digital cash.

Now, whether the designers (Satoshi) didn't realize the power of immutability and thought that one could change things on the fly in the sense "let us already start with this test version, and move on", or whether they were more sophisticated and somewhat less honest in their sayings, is an open question - my idea is rather the former, but I don't exclude the latter.

In a sense, they were right, new systems have been developed, but they weren't bitcoin evolutions, but alt coins, because *changing* a coin is essentially impossible, but making a new one, is.

That said, as of today, there is not yet a solution for "digital cash" apart things like the LN, which re-introduce normal banking.