The vast majority of real world businesses create prices based on cost plus systems, not on supply/demand, which are generally impossible to measure directly. Another good chunk of smaller businesses simply copy the prices of larger businesses, at least in b2c markets. Sure, if their goods are not selling, they might reduce price, but they might try other tactics as well (marketing, targeted discounts, etc).

I always thought of supply and demand as more defining a limit that the price approaches as the number of transactions and the size of the market approach infinity, barring structural obstacles or persistent information asymmetry to prevent it than as something that was supposed to happen immediately on any given transaction.

these "other tactics" are just attempts at increasing demand. Cost plus is how many business set prices but that is entirely separate from what the market decides. If cost plus is not an attractive price, it won't sell, because the demand is not there.