That's largely my recollection too. HyperCard was hugely popular, especially as an introduction to programming for kids, but the Quadra Macs and their kin introduced color and everyone wanted color. HyperCard never got a native update for it and it was the number one feature everyone wanted.

There was a related product (SuperCard?) that offered color. I remember trying it but it was clunky. I don't remember why, but in any case, it never took off.

There was also the matter of HyperTalk's limited API. There was a market for ... extensions, I think they were called? Some developers really dominated that space for a while. (I wonder whatever happened to J5erson? He was brilliant.)

Extensions were commonly written in Pascal and could add a lot of capability to HyperTalk, and were a great stepping-stone for people that wanted to explore programming beyond HyperCard.

Decker looks like it has a lot of the good things from HyperCard -- simplicity, portability. Kind of a shame it isn't using something closer to HyperTalk though. It really was a nice language, for what it was.