It was around 2017 that rules were changed and many credit card companies had to change their loyalty schemes. I cannot remember the details.
In 2018 credit card companies were required to assist customers in persistent long term debt by offering easier payment options and reducing or cancelling interest payments. This made cards less profitable for them and loyalty schemes had to be adjusted accordingly. Basically, the poorer customers with balances rolling over each month at 20% interest weren't paying for the perks of the better off customers who paid in full each month.
https://www.fca.org.uk/news/press-re...introduced-fca
Airlines would rather you use your miles for the premium cabins on leisure routes. These are likely to be empty anyway, and the top tier FF going on holiday with his wife burning up his points is far better than having him try to use them for a business class seat on routes such as LHR - JFK. Hence leisure routes have good availability and attractive redemption rates.
I confess to having been a miles whore many years ago, concentrating only on my monthly total. Now I don't use CCs for any foreign spending even if they offer double miles as Wise, Revolut or similar have better rates and no 3.5% fee. I'll also shop around for the best fare rather than stick with an alliance.
Basically adjustments are another form of shrinkflation. Reduce the product size or reduce the quality of the ingredients for the same price.