It's standard in the USA because of government policy. (Mainly Fannie Mae and Freddy Mac). 30 year fixed rate wouldn't exist in the free market.
https://www.marketplace.org/2018/10/31/why-do-we-have-30-yea...
https://www.marketplace.org/2018/10/31/why-do-we-have-30-yea...
* https://www.ratespy.com/best-mortgage-rates/10-year/fixed
* https://www.ratehub.ca/best-mortgage-rates/10-year/fixed
For down payments <20% mortgage insurance is needed (usually from the federal government subsidiary, like Fannie/Freddie), but not for larger down payments: that's all free market.
Some institutions offer 18- and 25-year terms.
Case in point: there is no such government policy in Spain, yet most banks happily offer fixed rates.
You just need to hedge the fixed mortgage you are selling and add some interest to make profit.