This is a delicate situation. You technically could tell them off, but will lead to better outcomes? People typically do not just change behaviors after being lectured. (See backfire affect on https://en.wikipedia.org/wiki/Confirmation_bias)
You could bring up the problem of no results, but to get behaviors to change you will need to follow through with action. Think of yourself acting in the following roles and it might produce better results.
1. As a Leader and/or Volunteer
Whether or not you are on the board yourself, you have an obligation to do something, made evident by posting your question here. I notice you said,
I'm starting to believe that it isn't the members with a lack of motivation, but the leaders themselves falling short in their ability to inspire and lead to produce results.
It sounds like this board needs some guiding visionary (such as yourself) to set the mission, vision, and values and some accountability to stick to them. Make a plan that lines up with the organization's mission, vision, and value statements. If they do not have one, or it is poorly understood, update it or create a new one. Make plans that carry out the mission. Stick to the plans. Make time-bound plans in monthly and yearly intervals or whatever is appropriate for the organization. If events have poor results, find out why. Talk to people. Why did not people show up? Who dropped the ball? Could anything have been better managed?
2. As a Coach
Do not complain and do not focus on the negative. Start with the end in mind. Focus on doing the right thing first, and doing it well second. Are there specific behaviors you are noticing that need to be changed? What behaviors should be happening? Ask the board a lot of questions to get them to see and understand how things need to operate. Draw the solution out of them and be specific. Focus on the goals and outcomes, not the list of things you dislike irregardless of their legitimacy.
3. As a Manager
Are events thoroughly planned out and prepared for? Everything from marketing, buy in, market research, to focusing on what your members want should be listed and well thought out as well as every calendar detail. It could be that there is poor planning taking place (in combination with a lack of inspiring vision). Sometimes just having a well executed program of events is all it takes to bring an organization back together. And, to point #1, getting members to volunteer to lead and holding them accountable as owners of those events can help even more. Asking members to help will build trust, accountability, and result in better events - just be sure to lead with the vision first.