It's never that simple, though, is it? Suppose that tool solves a problem that a $100/hour employee would have solved manually in a day. How long did it take the employee to identify and choose the tool, arrange the purchase, and then learn to solve the problem using it? Probably a few hours too. So that $50/month tool had better be useful for replacing that job several times in a year or it's unlikely to be a net win in terms of time and money. It's certainly possible that good tools are far better than that cost/benefit ratio and using them is easily justified, but I'm guessing that in these organisations with hundreds of different SaaS subscriptions only a few of them are in that class.
Of course the elephant in the room is that there used to be another alternative, which was buying a tool outright for say $1,000 and then using it indefinitely, which would be a financial win compared to an equivalent $50/month SaaS tool in well under two years. Yes, there are factors like CAPEX vs. OPEX to consider so this isn't so simple either, but ultimately paying much more money for the same thing is still paying much more money, however you slice it.