72 hours is quick. A week is more reasonable. I had one company try to pull a 48 hour decision on me and I straight up told them I was declining the offer if they didn't give me more time to consider it. They backed down.
This is a decision that will impact my career trajectory, and I may have other offers coming. So yes, I want enough time to consider all options before making a decision with ramifications that will last years.
I'm not sure it's so much time to consider as time to tell any others companies you're also through some part of the process with (especially if you're already through interviews) that they need to make a formal offer to you now or you're going elsewhere.
Maybe it's just me but if you just have one offer letter in hand and have probably already thought about what it would take to take an offer, I can almost certainly make a decision in an evening.
But seriously, if you are in a business that has been around a while (20-30 year range) and likes folks to stay a long time - you just are not as interested in hiring the type of folks who want to set off bidding wars, drag out offers, counteroffers, job hop etc.
If the candidate is great, can always just say, would love to talk through an offer that would work for you. If they are reasonable - bingo - everyone is happy. Again though, these offers end up with a short expiration so I can get to next person if you don't want position after all that.
But I also pull down posting pretty promptly, do a quick 5 minute phone screen with lots of folks right away (same or next day after application) etc. so they can move on too.
Yes, it's a function of there being other companies in the mix. I've only been in that position once right out of engineering grad school. As it turns out, the position I (probably incorrectly) wanted was from the government and they didn't have any flexibility. (This was also in the early 1980s and the salary figures would seem hilarious to people here although I assume software wasn't much different at the time.)
This is a decision that will impact my career trajectory, and I may have other offers coming. So yes, I want enough time to consider all options before making a decision with ramifications that will last years.