As a software engineer with a long track record, I somehow only just realized this about myself within the last couple months.
With the two fresh data points I have in mind, it wasn't about perceived likelihood of an offer, but about perceived likelihood of it being a good situation if I accepted the offer.
Delays (especially after a great initial call) can be felt as signal about how much they value the role, whether they're excited about me specifically for it (both of which can make the difference between a great role and an awful one), and how well they can execute (e.g., do they have a clout deficit or a huge-corporate bureaucracy that would also be a problem getting things done there).
And if there's a recruiter, HR middleperson, or other communication barrier -- blocking the normal ability to read people and pick up on clues, from direct interaction with a hiring manager or team member -- this signal can be all we have to go on.
But whatever the goal of your organization, achieving that goal is going to depend on the people you hire.
Nobody in the company "makes money" (unless the company is a bank, then they literally do, by giving out loans). The people perform various functions and the money made or lost by the company is a result of a sum total of their actions.
It's not difficult to find companies that cut costs in order to increase profits only for it to backfire and result in less money or even bankruptcy.
Additionally a responsive and clearly communicating company is always a good sign that they really need to fill the role. It is always a plus if I go from hiring manager/recruiter straight upper management interviews in a matter of days.
Additionally the quicker the employer response the more likely the applicant is mentally primed for the responder and does not yet have their mental/time bandwidth taken by competitors.
I've noticed my interest in a job tends to drop consistently the longer it takes for a response. This isn't surprising at all. I don't think it's because we're fickle, it's more that right when you apply you can picture what it might be like to start working for the company and start to identify with that future. As the days drag on, that picture seems less and less likely to happen.