This is Hulu + Live TV's second price hike this year, with a $5 increase in January, followed by this twice-as-large increase, which is supposed to take effect on December 18.
In the email, Hulu says this increase "allows us to continue delivering the best live and on-demand TV experience for you." However, as a the price keeps going up, the price advantage that a "skinny bundle" of TV channels offers over plain old cable starts to shrink.
Hulu's ownership has also been changing, with Disney becoming a majority shareholder following its acquisition of Fox, and then taking full operational control of the company earlier this year. Hulu is part of Disney's broader streaming strategy, which saw the company launching its own Disney+ service earlier this week and offering Disney+, ESPN+ and Hulu (without live TV) together in a $12.99 bundle.