A scientist would most likely need to update her model when it has become too simple. no longer supports the latest results. reduces the need for verbal explanation of data. no longer appears interesting.

It no longer supports the latest results.

Explanation:

When a model does not coincide or can not explain the latest results in research, it means that the model is not suitable anymore and a new one that can justify the new results, as well as the old ones, has to be made by the scientific community. When this happens, there is a paradigm shift from the old model to the new one.  During this process, the scientific community divides into two groups, the ones in favor of the new model and the ones that are against and state that the old model can still solve the problems. It takes time to settle the novel model in the scientific community and society.

it is a limiting nutrient limited by a single nutrient in the ecosystem, & the single goes very slow.