The cost is absolutely not prohibitive, it's about $1-2/sq ft in a new home or $5-6/sq ft if you're retrofitting an old home[1]. For a new 2000 sq ft house that would be around $4000 dollars. Probably <1% of the overall house value given recent housing prices.
This would depend on house prices. Where I live, you can buy a 2000 sq ft house for $300K or less. That's 1.3% increase in price to add sprinklers, and I would wager that 99% of homeowners would prefer not to spend $4K on this.
[1] https://www.bobvila.com/articles/465-residential-sprinkler-s...