How to Improve Seller Engagement?

One of the things that I have personally been challenged by is addressing the lack of a sense of urgency with some leaders of businesses that my company is engaged with to acquire. Specifically, organizations where there is a Letter of Intent or similar in place and we’re actively moving toward deal finalization. It’s important to clarify that the challenge most often occurs when the leaders are not intending to join our business. It’s almost as though once they confirm their decision to sell, they lose their motivation to do the work (usually hard work) of pulling together data, meeting to discuss pre-integration, etc., etc.

Does anyone have any tips on how to successfully encourage seller leadership engagement to keep M&A activities on schedule?