It wasn't the lack of slots and cards, it was the hardware was too magical and hacky. Basically it was over-engineered so much it couldn't evolve.
People made code that depended on those hacks and magic. If the coprocessor doesn't work the exact same way in the future then everything breaks. That's fine if it's doing something simple like displaying a big array where each byte was a pixel or RGB value because you can easily make that backward compatible. Instead it was doing things like running code between scan-lines and using 5 bits per pixel.
A new display chip would basically have to include the old chip in its entirety just to be backward compatible. All the Amiga hardware worked like this.
People made code that depended on those hacks and magic. If the coprocessor doesn't work the exact same way in the future then everything breaks. That's fine if it's doing something simple like displaying a big array where each byte was a pixel or RGB value because you can easily make that backward compatible. Instead it was doing things like running code between scan-lines and using 5 bits per pixel.
A new display chip would basically have to include the old chip in its entirety just to be backward compatible. All the Amiga hardware worked like this.