My ex therapist also took a lot of vacation time. A ton of it. Even in the countdown to her leaving her practice, after having several vacations already during the year and when I thought we had only 4 sessions left, she sprung it on me that she had decided to go on another vacation for two of those weeks and we would only have 2 more sessions!
There isn't really much you can do about it except explain how it is hard for you. But that doesn't obligate them to change anything about it. They are not responsible for us, and their own lives take priority over ours, which is just how it should be.