Volcano
It is very easy to sit here and criticise any airline, but this volcano activity is a new problem for the industry. As peak season approaches, it will be even harder to get out of trouble than a few weeks ago.
One example would be to leave a spare aircraft at (example Tenerife) with crew to use for shuttles to (which ever airport is open) etc, but in the summer, heading for the peak, how many spare aircraft would there be?
Airlines are good at dealing with a couple of cancelled flights caused by tech issues, crew sickness etc, but to cancel hundreds at a time is a whole new ball game.
I know it is heartbreaking when your holiday is cancelled etc, but a reminder to all that the ruler of the planet is indeed Mother Nature!