Hmmm I think people, and animation directors, as a whole are more awestruck by beautiful, animated details and colourful scenes than the actual story itself. As a result, we keep getting better animation quality while the plot remains subpar (with the exception of Kimi No Na Wa).
This movie starts off with Sophie, a young girl who seems to be old at heart, doing her daily job like any other adult- and unlike a typical young girl. Then Howl swoops in suddenly to get her tangled in his magical troubles, and she gets cursed by the Witch of the Wastes to lose her youth and so her story begins, to find a way to break the curse and tumbles into Howl's Moving castle. But then, later on, the plot thickens *drumroll* because our magical boy is used in the nation's war (why? I didn't see any other wizards/ witches in the war?) and his friend, the fire, holds his heart (again why?) The entire movie rumbles on in a rollercoaster, racing and then, quite suddenly, you arrive at the ending. Sophie, for some weird reason, opens the door to go check outside when there are air raids and bombs dropped (why?) and lets blobs in (why not change the door colours?) and eventually, Howl's castle crumbles and Howl succumbs to his defeat while the fire burns out under water (lol). It hurt me a bit because Howl so painstakingly redecorated the castle to make it extra comfortable for the extra people living with him and even redecorated Sophie's room to make it look the same as her old room for her. But...anyway it's all destroyed by Miss Sophie who finds him in the end and brings him back to life, kisses everyone and they change back to their original selves (-_-) except for the Witch of the Waste, who is forgiven and travels with them.
I'm not even sure how Howl (who said he cared more about beauty in the beginning and in the bathroom scene) fell for Sophie who's old and wrinkled. There was no clear explanation as to how his feelings towards her changed, which is such a missed opportunity to be honest. And I think she regains her youth at times when heart is full of life and love (and while sleeping too because she's at peace or something? Lord knows) and turns back to old age again. When your attitude towards life changes for the better, I agree that it does slip back into doubts but really, not quite as dramatically often as Sophie and her old age curse. I have no idea what they wanted to portray because a lot of times throughout the movie, to me, the ageism reeks.
In English folklore and fairytales, there is a clear outline of who does what and why they do it. In Japanese animated movies, all I see are breath taking animated sceneries and landscapes with not much essence/ substance for the viewers to understand what's going on and way too little character/ relationship growth and development. Honestly, not worth the hype but you can watch this once I guess.