And also because when people try to use neopronouns they take as much flak for that if not more. Imagine this same argument: "I'm not used to these newfangled pronouns. Why can't they just use normal ones?"
As someone speaking German, a brutally gendered language, let me tell you, they/them is awesome and I'd love to have something similar in German. There is so much fighting and discussions about "gendern" and it consumes so much energy that could be better spent elsewhere. And conservatives are having a field trip with this.
Looking for a new word is equally as hard if not way harder than using what already works fine.
Yes I would love for the German language to have an equivalent for they/them. It's also so awkward talking about someone who is non binary and neither uses he/him nor she/her and you always have to refer to them by their name.