If people don't care about scenarios, they don't bother to complain. Only a very small percentage of players has completed all scenarios in bronze, so not many people bother with those. I think the scenarios we have in the game are too easy and if they added scenarios with the same difficulty, that would be a waste as well. As mentioned, custom scenarios would be a good option.
First off, it's a videogame.
I completed a most timed scenarios in gold but nice looking is debatable (very basic). The habitats themselves looks decent and the animal welfare is good, so animal care aspect is covered.
The amount of scenarios/storylines/career missions in the base game are very limited and if you are looking for a more lineair game, PZ doesn't offer much. Except for scenarios, every mode is a sandbox.
Only the scenario has required (mission) objectives and you can complete all scenarios in gold in a few hours.
Every scenario can be completed in 30-45 minutes, maybe even faster.
At the least the timed scenarios offer something new and if you don't make it in time, you can try again to optain gold. The normal scenarios don't invite that.