Why gradle does not use cache in docker

But why the following work:

FROM node:10-alpine as node
WORKDIR /app
COPY package*.json ./
RUN npm install 
ADD . .
RUN npm run build

The last line npm run build will reuse the node dependencies downloaded in the step npm install.

The only difference is that the node dependencies will be saved in the current directory while gradle dependencies will be put outside the current directory.