Holy Wars are Subjective
Nick's elastic tabstops are an amazing concept that could help a lot of people agree on a workable solution, though I highly doubt it would entirely end this Holy War: it is, after all, also a matter of taste and many programmers will not move an inch from their position on this matter, even at the cost of compromise. So that would be a first reason.
For instance, a lot of people on the "spaces" side will still dislike it as it requires an additional piece of logic in your software for a decent rendering (e.g. simply viewing a changeset in your SCM's webview).
But the most obvious reason is just its technical barrier to entry: it's a fundamentally different concept from what has been implemented for a number of years (if not decades) in IDEs and text editors. It would require to rewrite some of them to process lines in a fairly different fasion, which makes it difficult for older and bigger systems that have a higher chance of suffering of deep and tight coupling in their line processing code. It is, however, a lot easier to do when you start from scratch (think of Nick's demo or of Go's tabwriter package).
For a personal anecdote, I remember approaching the author a while back to ask if there was any emacs support in sight, and in this particular case he mentioned this as the reason for it not being trivial. He also asked for help from the community to help implement this feature and bring it to the masses.
Do We Care Enough?
A third reason, is that some developers are not that hung up on the matter and don't really care so much that they would go the extra mile to support the effort. In most cases, the spaces-vs-tabs conflict is not a business blocker, so there's not so much drive behind the issue.
If you want it, you'll have to fight for it. Which is doable in open-source software. And if you change enough of these, closed-source ones will have to follow at the risk of losing to some of their userbase, if an ever so small part of it.
So, if you want it, give Nick a hand.