But to be operative in this way, you must be talking about a very high volume. Millions of units, or close.
My point was not that cost never matters, just that $1000->$100 is not the same as $10->$1. If your weather station startup is using $10 microcontrollers, getting that down to $1 is probably not important. If you are building 10 million weather stations, it is important, but this is a pretty specific scenario that doesn't apply often.
We say something similar with PC pricing. The cost of a functional PC never stopped falling, but that stopped being as important once a certain threshold was reached. Projects like RasberryPi do take advantage of continued cost reductions, but Pi is marginal relative to earlier cost reductions cause an explosion of PC use cases.
That means if you are making a new gadget to send out to users, and hoping to make money on data collection, a subscription service, ad revenue, etc., the unit cost of the hardware is critical to the business case, even if it isn't much money overall.
Try telling investors "we made this weather station, and we will make money by selling data to NOAA".
The very first question will be "how much does each station cost", and "how much will NOAA pay". Nobody asks how many engineering hours you spent writing the code to fit on the microcontroller, because the assumption is that in any successful business that becomes irrelevant.
Perhaps investors should accept "Each weather station costs $1000, but we think we can get it down to $10". But most investors won't believe you if you say that...