This is basically why some researchers gravitate towards certain model systems in terms of abstracting the problem. It is just easier in terms of approval the simpler things get and you can basically grasp at the same sort of questions since basic cell biology is so conserved. You can do things like grow up a generation of transgenic yeast that glows green under UV light and then pour bleach over it and throw it in a carboy for disposal over the week without anyone needing approve anything but the form for the carboy to get incinerated. You try and write up a proposal for transgenic mice it might take months since the IRB needs planets to align for meetings to be scheduled. And you are paying orders of magnitude more for orders of magnitude fewer individuals in your sample that will take orders of magnitude longer to get data, than an organism that can measure reproduction rates on the log scale over hours and cost pennies on the billions.