It takes a considerable amount of time to get a backer build ready and working. Each new backer build we release potentially takes development time away from the finished game.
There was never an explicit promise of how many backer builds there would be, just that there would be early access (which there has been).
I can’t help noticing that you’re very hung up on Epic and external funding. That doesn’t really have any relevance.
As I’ve said before, the person originally working on the roadmap is no longer with the company. We do have someone new, but they have a hundred other things to do. We’re still an indie company of the business side of the team (non-developers) is only 4 people. We’re just months out from launch and we have a lot to do including getting all of the rewards ready.
We would love to have the roadmap up to date, but it just isn’t a top priority right now. In addition to that, roadmaps are always meant as a guide and often change constantly. This is why you will find most studios are vague with dates or information, some choosing not to give any at all. As soon as you give a date or show something in a roadmap, people see that as a promise, expect it and then get disappointed.
You mention yourself that trust can be broken by breaking promises - so this is another reason not to provide information which may not end up being accurate by launch.