I understand where you are coming from logically, although I am of the belief that this is not ethically acceptable. Ethics aside, jumping straight to human testing without assessing safety wouldnt really save that much in terms of cost and time to develop a drug, compared to developing better in vitro and animal models of disease
safety studies are not the largest driver of cost and duration of drug development. failing a later stage human study that assess effectiveness is a much bigger needle mover in terms of cost, as is the arduous and painstaking process of early drug discovery and development. human studies of effectiveness cost $15-500M+ and can take 3-7 years. putting a drug in humans that has a low probability of success is the most value destructive thing you can do in pharma. the other big cost driver is early research in drug discovery and development. understanding the biology and chemisty, developing assays, and screening compounds can cost $15-20M+ and take 5+ years. by comparison, animal safety studies cost maybe $5M and take a year or two
For more context:
There's an important distinction to be drawn between two main types of animal models: models assessing drug "safety", and those assessing "effectiveness". the models of effectiveness are very poor and of questionable value in some cases, although they are often the best we have. animal models of effectiveness are not literally required for FDA approval, although in reality they pretty much are
animal models of safety, however, are required by FDA, and rightly so. they are of much greater value. generally you must do studies in a small species like a mouse as well as a non-human primate. these "toxicology" studies basically entail dosing animals with huge amounts of drug, way more than you'd dose in humans, and then seeing what doses are not toxic. this informs the first dose youd do in humans
the initial human studies are not done to study effectiveness, but to study safety. based on the data from your tox studies in animals, as well as other studies, you gradually dose cohorts of patients with higher doses, watching carefully for safety signals.