They do not consider it because it does not exist. I feel very confident in saying that the number of folks who will stop going to Epcot because of the acts departing is equal or less than the number of folks who will visit to see the new acts and mostly amounts to friends, family, and die-hard friends of the acts themselves and NOT the random/average park goer. Honestly, the folks in this thread are likely the most angered over this change (who aren't directly affected) and how many people here are planning to cancel a trip because of it? Not just willing to say they are in a forum thread, but actually going to cancel?
You're missing the point. People (generally) don't visit theme parks for any one specific element, but rather the total experience of all attractions and entertainment (and shopping, dining, etc.) in the park. You can (generally) remove any one experience - even major attractions - without more than a negligible (if any) decline in attendance. The loss off a headline attraction makes more of a difference, but even then (with the exception of parks (Animal Kingdom) where there is such a dearth of attractions that there is nothing to really pick up the slack) guests aren't likely to start cancelling trips.
But Epcot isn't losing one element; It is losing several - but far more critically, the park's experiences have already been cut to the bone. Remember the Lights of Winter? Neither Off-Kilter nor Wonders of Life, for instance, matter as much in isolation, but as part of the 'whole' park experience, it does. Replacement entertainment helps, but it likely won't start right away, and are an unknown element; The outgoing acts are well-liked, and Disney has a poor track record when it comes to replacing park attractions and experiences.
Epcot has already been compromised, cheapened, and dumbed-down to levels we would never have thought possible for what was once a special park. This isn't just about the loss of Off-Kilter and the other acts, but rather the bigger picture of why and how such decisions are made.
Those of us on this forum seem to always forget that we are a tiny, tiny minority. Most of the folks, a vast, vast majority, won't notice nor care about the entertainment changes. It's this way really with just about most of the stuff we wail and moan about- hub redesign, entertainment cuts, refillable mugs, store closures etc. They only notice the big stuff- new attractions and lands. I love our passion for all of this but 99% don't notice, care.
While most visitors to Walt Disney World will not be aware of such changes prior to their actually being in the parks, once there don't think all the little cuts and compromises to the experience go completely unnoticed. Many people will not quite be able "to put their finger on" what's wrong or what is missing, but they do not miss the overall impression of a cheapened experience. Combine that with rapidly increased prices, and the impression guests take away from a WDW vacation is nothing like what it once was. That will come back to haunt The Walt Disney Company soon enough.
I DO think that refreshing and changing out the performance acts is the easiest and cheapest way they can contribute to keeping Epcot feeling fresh.
That, in a nutshell, is exactly the problem. Disney, as usual, takes the easiest and cheapest way out to try and keep a stale park looking 'fresher' than it really is.