Are your neighbors getting lots of hummers, and are hummers using the native vegetation a lot, or are there just fewer hummers in general in your area? If they're still around and just not using your feeders, I don't have an answer, except that perhaps they're getting all they need elsewhere and haven't needed your feeders. We noticed that our hummers didn't use our feeder (even though they found it quickly) much at all until a lot of the abundant spring bloom had passed. I suppose it's possible there's a problem with your feeders not being clean enough (they can be sensitive to that) but if you've been feeding a long time, you already know about that. I know, this doesn't explain why they were so thick around your feeders in the past and not now; I'm just speculating on what they might be doing instead.

If hummers in your area have declined, local birders and/or a local wild bird shop may have information about what's going on.

Best of luck!