On October 11, 2017, Southwest announced that it was going to start serving Hawaii. 17 months later, they are now flying to Hawaii.
Flying to Hawaii is a less complex process than flying to Europe. For starters, there aren't slot restrictions in Hawaii, nor are they dealing with the laws of other countries.
Anyone expecting JetBlue to be able to start service to the UK prior to 2021 did not have a realistic expectation.