Disappointed but not surprised about reactions to this, what a waste to get cast members back and not use the opportunity to do something special.
Why do studios keep doing this? Because people my age can't accept that the past is the past, there's an insistence that everything "back in MY day" was great. We are the generation with the most disposable income at the moment which makes us a target audience for studios to shoot in the nostalgia sack, that sack leaks money when shot enough.
Over the last few years I've realized that most (not all) of the entertainment I grew up with in the 70s/80s was at best a "product of it's time" and at worst just crap.
I haven't watched the original Willow in 15 years or so, I might suggest it to my daughter for one of our reviews (she loved it when she was 5), I'm willing to bet it holds up, that doesn't mean it needs another chapter decades later.