In the past users of enterprise software had to accept terrible UI. Times have changed, expectations have increased and users have more of a voice than they did in the past.
Users grumbling about UI is background noise for every product. In an enterprise grumblings turn into leverage for power players within the organization to achieve their personal agendas.
Imagine a leader that thinks it would be better to replace your product with a customized version of Sharepoint or they want to re-compete your contract to give your competitors a good look. Lots of users grumbling about bad UI will be used as supporting evidence that their idea is the right move for the organization.